How do I fix a pool liner that is pulling away from the wall?

Fix the leak first. Find it with a dye test or by looking for air bubbles, then patch it with a vinyl patch kit or pool repair tape. Refill the pool slowly so water pressure pushes the liner back. If it doesn’t settle, use a shop vac on the skimmer to create suction while you fill. Don’t use weights or clips — they’re just band-aids.