2 Digit year when importing

Perhaps the simplest way will be using background error checking as here https://support.office.com/en-us/article/Convert-dates-stored-as-text-to-dates-8df7663e-98e6-4295-96e4-32a67ec0a680

That's important in your Import Text wizard you select to import as text, not as general. With this option query itself won't make any conversions.

After that copy/paste first cell in your column to any another empty column. You shall see error mark on top left level of the cell where data pasted. Next select and copy/paste the rest of your data under this cell - now all shall be marked by error. Select all cells with error, click on error button menu and choose proper conversion

Here is the result (i'm on ISO date format)

If you have dates both before and after millennium you shall process them separately. Column into which you paste shall be in General (by default) or Date format.

I would just run some VBA after the text import. If you run the code below, it will ask you for the TWO DIGIT transition year between 1900/2000. For example, enter '50' not '1950'

Option Explicit
Option Base 0
Option Compare Text
Option Private Module

Sub FixTheDates()
''''''''''''''''''''''''''''''''''''''
' Allows changing dates with two-digit
' years, using the transition year of
' your choice. The user will be prompted
' for the transition year.
' Author: Chip Pearson, chip@cpearson.com
' License: Explicit Public Domain
''''''''''''''''''''''''''''''''''''''

    Dim Year2000 As Long
    Dim R As Range
    Dim RR As Range
    Dim Cutoff As Long
    Dim S  As String
    
    ' ensure Selection is not null
    If Selection Is Nothing Then
        MsgBox "The 'Selection' object is null (Nothing).", vbExclamation Or vbCritical, "Null Selection"
        Exit Sub
    End If
    
    ' ensure selection is an Excel.Range, not some other object (e.g. a Shape)
    If Not TypeOf Selection Is Excel.Range Then
        MsgBox "The 'Selection' object is a '" + TypeName(Selection) + "', not a range of cells." + vbNewLine + _
            "Please select the range of cells and run this procedure again.", vbOKOnly, "Invalid Selection"
        Exit Sub
    End If
 
    
    ' let the user choose the century transition.
    Cutoff = 30 '<<<<<<<<<<<<<<<< two digit values LESS than this are considered 1900 century.
                ' two digit values GREATER THAN OR EQUAL TO thias are considered 2000 century.
                ' E.g. Cutoff = 30 implies 26 means 2026 and 36 means 1936.
    
    S = "Enter the two-digit year at which the century cutoff occurs." + vbNewLine
    S = S + "Two digit years LESS than this number are consider to be in the 2000 century." + vbNewLine
    S = S + "Two digit years GREATER THAN OR EQUAL TO this number are considered to be in the 1900 century."
    
    ' prompt the user. the "50" is the default, but if the user clicks Cancel,
    ' the result is 0 and we get out.
    Year2000 = Application.InputBox(S, "Year Cutoff", "50", Type:=1)
    If Year2000 = 0 Then
        ' user clicked cancel
        Exit Sub
    End If
    
    ' ensure valid range
    If Year2000 <= 0 Or Year2000 >= 99 Then
        MsgBox "The value '" + Str(Year2000) + "' is not valid." + vbNewLine + _
            "It must be between 0 and 99 (exclusive).", vbExclamation Or vbOKOnly, "Invalid Data"
        Exit Sub
    End If
       
    ' set our range of cells
    Set RR = Selection
    If RR.Cells.Count = 1 Then
        ' if there is only one cell selected, the user likely forgot to
        ' select the proper range. ask her.
        If MsgBox("The selection contains only on cell." + vbNewLine + _
                "Did you forget to select the range?" + vbNewLine + vbTab + _
                "Click 'Yes' to continue with once cell or click 'No'" + vbNewLine + vbTab + _
                "to exit so you can select the proper range.", _
                vbYesNo Or vbQuestion Or vbDefaultButton2) = vbNo Then
            Exit Sub
        End If
    Else
        ' only one Area allowed
        If RR.Areas.Count > 1 Then
            MsgBox "You may only run this procedure on a single area (a rectangular range).", vbOKOnly, "Invalid Selection"
            Exit Sub
        End If
    End If
    
    On Error GoTo ErrH:
    With Application
        .EnableCancelKey = xlErrorHandler
        .EnableEvents = False
        .Calculation = xlCalculationManual
        .ScreenUpdating = False
    End With
    
    ' restrict our search cells to numeric constants, ignoring formulas
    ' and non-numeric data.
    Set RR = RR.SpecialCells(xlCellTypeConstants, xlNumbers)
    
    ' loop through the cells and test and fix the years
    For Each R In RR
        If Year(DateValue(RR.Text)) Mod 100 >= Year2000 Then
            R.Value = DateSerial(Year(RR) Mod 100 + IIf(Year(R) Mod 100 > Cutoff, 1900, 2000), Month(R), Day(R))
        End If
    Next R

ErrH: ' We're done!
    With Application
        .EnableEvents = True
        .Calculation = xlCalculationAutomatic
    End With
End Sub