I put it on top of a colander that was just a bit smaller around than the record. I put a block of wood in the bottom as a stop and put a coffee mug on top of the record. I used a heat gun and went around and around the record being careful not to get the record too hot and thus melt a hole in it. When it became pliable enough I pushed down gently but firmly on the mug until it hit the wood stop. then I held it that way until the record firmed up.
Q