can you please tell me how i can perform this formula in tableau dekstop (Audit Type = Update if Type = 'U', Delete if Type = 'D', Insert Type = 'I', )
Impossible to tell you exactly without seeing the structure of your data in Tableau as a Packaged Workbook and maybe even reference to the data you used to generate the formula you previously made.
Generally speaking, you might want to start with understanding logical calculations Understanding Logical Calculations | Tableau Software
Perhaps a calculated field with the formula:
IF [Type] = 'U' then 'Updated' ElseIf [Type] = 'D' then 'Delete' ElseIf [Type] = 'I' then 'Insert' End