return a list in a multi-line field

I'm trying to fetch and return a list into a multi-line field, but can't figure out the script.

Select a region (radio button)

fetch a list of records = region (which I can already do)

Return list from the records that = region in a multi-line field (rather than a drop down lookup) so they are easy to see

I don't need the list to be selectable, but rather are just for reference.