In addition to @steve359's wonderful advice if the laptop is a 2012 model, then you may still be able to get an official Apple battery replacement. I highly recommend an official Apple battery if it is at all possible. If you are unable to get an official Apple repair to due COVID19, then you could order a third party replacement battery from OWC. The quality of third party Lithium-ion batteries is very poor even from a such a reputable vendor as OWC. Results vary greatly even with OWC batteries.
If you do replace the battery yourself I would highly recommend keeping the original swollen battery safe so you can later get an official Apple battery. Apple needs the original battery in order to provide you with an official Apple battery repair.
Regardless, If it was my laptop I would remove the swollen battery and put it somewhere safe (inside a metal tin would be best to keep the battery from being accidentally punctured or compressed. You do need to be extremely careful when handling a swollen battery as you want to avoid puncturing it or applying any pressure to it. At least with the battery removed and safely stored you can continue to use the laptop (perhaps a mouse will be needed). Just be careful to hold the bottom case as you remove the screws since there is a lot of pressure on the case. It can cause the screws to go flying across the room.