Power Query - String as Table name

Deleted 

Here's an option

let
   
   MyTableRecord = [Table1 = Table.FromRows({{1,2}, {"a", "b"}}),
                    Table2 = Table.FromRows({{2,3}, {"a", "b"}}),
                    Table3 = Table.FromRows({{3,4}, {"a", "b"}})
                   ],
   TableSelect = Record.Field(MyTableRecord, "Table" & Text.From(SelIndex) )
in
   TableSelect

I have to thank Imke https://www.thebiccountant.com/ for this approach

Deleted 

I'm not sure it's possible to make reference such way on any name, but it's possible to choose from predefined names, like

let
    nIndex = 2,
    Table1 = Table.FromRows({{1,2}},{"a","b"}),
    Table2 = Table.FromRows({{3,4}},{"a","b"}),
    Table3 = Table.FromRows({{5,6}},{"a","b"}),

    // Select from environment
    TableSelect = Expression.Evaluate("Table" & Number.ToText(nIndex),
        [
        Table1=Table1,
        Table2=Table2,
        Table3=Table3
        ]
    ),

    // Select by function, but actually it's the same
    TableSeletByFunction=SelectMyTable(3),

SelectMyTable =
    let fnSelectTbl = (n as number) =>
        let
            tables = {
                {1,Table1},
                {2,Table2},
                {3,Table3}
            },
            ReturnTable = List.First(List.Select(tables, each _{0}=n)){1}
        in
            ReturnTable
    in
        fnSelectTbl
in
    TableSelect //TableSeletByFunction

If Table(i) are returned by another quires we may use #shared environment, when it's not necessary to predefine the list of existing tables.