replace value in an existing column based on another column using if statement

[Lena1]

The formula below does not replace value. could you please help to correct formula?

= Table.ReplaceValue(#"Sorted Rows", each [Assignment], each if Text.Contains([Assignment], "Material S") then "A9 self-assessment" else [Tax Code], Replacer.ReplaceText, {"Tax Code"})

Thank you.

[Ahmedx]

Share some data to work with (in a format the can be pasted in an MS Excel file) and show the expected result.