The address to the Stevens Point Wisconsin Kingdom Hall is:
3600 Northpoint Drive, Stevens Point, WI 54481
Since his apartment is accessed from the back of the hall the address could have a "A" behind it or something like that.
I would leave it as 3600 and put Circuit Overseer in Bold Letters so the elders can forward appropriately.
Note: Not all Halls have actual mailboxes so the letter might be delivered or returned because dut to a lack of a mailbox.