Southwest stopped allowing that about 5 years ago. Now, all funds must be used by the originally named passenger. One sort-of "work around" (not helpful for the OP) is to let the funds expire, then request reissue as a voucher, usable by anyone. But the cost for that is (currently) $100, deducted from the funds balance. So not really worth it unless the funds definitely can't be used before expiration.