This enhancement is a coreBOS Updater changeset which adds a user picklist to the calendar records Follow-up block. That will permit you to select a user for the follow-up record.
Two more steps must be taken for this change to work.
The follow-up record is actually created by two workflows:
These two workflows must be changed so that the assigned user of the new record is updated from the new field, something like this next image:
Go to the coreBOS Translation module and create any translation records you may need. That will look something like this: