iPhone 14 pro Battery swollen

Express Replacement is when they ship you a replacement device before you send the current one back. This requires a hold of the phone value on a credit card until they receive the other phone in replacement.

You set up an Express Replacement by calling or chatting support. If you go into an Apple Store they are going to assess and if it can be repaired, they will do a repair on the necessary parts. In store replacements are only if it's beyond repairability.

If they repaired/replaced it and you’re still having issues take it back or contact Apple for support via phone or chat. You can only get express service if they are shipping you a replacement before you send yours in. Going to an Apple Store you won’t get a replacement device unless it can’t be repaired.

It’s called the Second Law of Thermodynamics. Anything that creates or uses energy does so with some loss. That lost energy is expressed as heat. So when you charge the phone it generates heat in the power source, heat in the charger circuit in the phone, and heat as the energy goes into the battery. The faster the charging, the more heat is generated. Likewise when you discharge the battery; not all of the energy from the battery gets to the circuits that use it. Some of it becomes heat.