Creating a drop-down list in excel using Python

Two excel files were merged using python into a new one. There are three columns in the new excel that should have a drop-down list. These columns are not empty, they're filled with data. Only a few cells are empty and need to be filled using the drop-down list. I can't send the code, data, or demo. It's confidential, so if you want to do this task I will share my screen and give you access so you can see and edit the code.