Whoever's ssn is on the 1099 enters the whole amount on their return. Then after you enter it, on the next page it will ask - Tell us if any of these uncommon situations Apply and pick the first one, I need to adjust the interest reported on my form.
Then on the next page fill in their amount as a POSITIVE number and pick the first reason "I received all or part of this for someone else".
Then on the other person's return you enter it as a 1099 Int and put their amount in box 1.
