Switch Statement (or Alternative)

In programming, you can do a switch statement where you feed it a variable and depending on what it matches, it’ll execute the code in that block. I want something similar on eSignature so that if one field matches a value, the other field is set to the value I set. For example, our courses have course IDs so if someone put’s the course on the dropdown, I want the relevant course ID to appear in the ID field.