If the battery is swollen up like a balloon.

If it looks normal then it truly is just the backplate warping and you can swap that out for cheap.

https://www.amazon.com/Original-Replacement-Housing-Nintendo-Backplate/dp/B07TCJCCF1

https://www.amazon.com/eXtremeRate-Console-Replacement-Nintendo-Switch-Kickstand/dp/B07MDK5MTM

Aliexpress even has limited editions and knock offs

On the off chance that the battery is swollen, prepare a metal can with sand or dirt; stuff it in there and call around for a proper disposal facility.

https://www.ifixit.com/Wiki/What_to_do_with_a_swollen_battery