Hi @BM_Girlracer,
A solution depends on how that table was created…
If it’s a supporting table and you’ve used “Enter Data” to create it, go to the Query Editor, select the Source step and add the column in the displayed dialog box
If it’s an externally sourced table you have 2 options:
First in Power Query , go to the Add Column tab and select “Conditional Column”
Second in Data view add a New Column using the DAX SWITCH/TRUE statement
I hope this is helpful.