Update value in a case created from record producer

Dear,

I take some times to look on various topics, but didn't find any answer.

I use the record producer "create case". On this RP, I added a variable set. I'd like to map the choice from the variable set to the created case.

How can I achieve this? using a catalog script? I don't know how to retrieve the created case sys_id.

From a Business Rule? I don't know how to retrieve the record producer variables?

Any other clue?

Many thanks

Séb