Usually pool liners are made of vinyl and if it is torn and you want to repair it, you will have to follow certain steps for the purpose. First of all you need to buy a repair kit from any shop that deals in the materials of pools and what you will have to do is to apply the bonding agent of waterproofing used for the vinyl patch material and the have to place it over the rip; you can use it even under water. You also have to smooth water bubbles or any kind of air that is present under the patch.
If you find that the liner is in extremely bad condition, then you should replace it altogether and should not try to repair.
If you find that the liner is in extremely bad condition, then you should replace it altogether and should not try to repair.