Easier said than done. Call Southwest at 1 800 248-4377. Redial 20 times until you get through. Wait 30 minutes on hold. Ask to cancel the outbound only. Hope the CSR does not also cancel your return.
What I would do: Just no-show the outbound. Your return will NOT be canceled. Southwest is different from other airlines in this respect.
Does that mean there will be no points until the outbound funds are used?