Power Query If Statement

Tony2021 

If I understood the logic of source correctly only one of AMT1, AMT2, AMT_New is not zero, thus you may simply sum them and replace with result AMT_New. Plus I'd clean the query, too many unnecessary steps

let
    Source = Table.Combine({Stampli_PQ, SAP_PQ_Drill_mod, SAP_PQ_Not_DD, BOA_PQ_mod}),
    #"Removed Other Columns" = Table.SelectColumns(Source,{"Vendor", "Amount Currency", "Payment Date", "Co Name", "Amount", "Amt", "Amt_NEW"}),
    #"Replaced Value" = Table.ReplaceValue(#"Removed Other Columns",null,0,Replacer.ReplaceValue,{"Amt", "Amt_NEW", "Amount"}),
    #"Changed Type" = Table.TransformColumnTypes(#"Replaced Value",{{"Amount", Currency.Type},{"Amt_NEW", Currency.Type}, {"Amt", Currency.Type}}),
    #"Renamed Columns" = Table.RenameColumns(#"Changed Type",{{"Amount", "Amt1"}, {"Amt", "Amt2"}}),
    #"Replaced Value1" = Table.ReplaceValue(#"Renamed Columns",each [Amt_NEW],each List.Sum({ [Amt1], [Amt2], [Amt_NEW] }) ,Replacer.ReplaceValue,{"Amt_NEW"}),
    #"Changed Type1" = Table.TransformColumnTypes(#"Replaced Value1",{{"Amt_NEW", Currency.Type}})
in
    #"Changed Type1"