Add_filter read user selected dropdown?

I should not have to ask this, but I am lost.

I cannot for the life of me find what built in “add_filter” code can be use to grab the value of a live dropdown form field, so that I can “if/then” input the value of another.

Thank you!

Hi TSCMarketing. Can you let us know what you are trying to accomplish exactly? We can help you with the best approach to the problem at that point. Thank you.