How do I change the battery? (it wont charge)

@launcey "i also did what they said that might fix" it will help if you tell us what you did, since we have no idea what YT video you watched. SInce you just had it repaired, you do want to make sure everything is properly connected. If it is all the way it needs to be connected, the issue could be your battery but it could also be the charging board. Not sure where you are located, but if it would be my phone,I replace both(depending on the cost) and re-evaluate.

Of course, you can also just replace the battery and measure the voltages on the battery connector. Ones without the charger and see what the voltage is and then with the charger. The voltage will have to be higher with the charger. If it is not, it is most likely a bad charging board. I would just not like changing the battery, assembling the phone and then finding out it still does not charge. I do not like to disassemble more often than necessary.

Since iFixit does not yet have the guides for that, I suggest you use this one for the battery and this one for the charging board

While you work on your phone, take lots of pictures. Once you are done with it, take those pictures and create a guide for iFixit. That will help the next person that has the same problem as you do. It's easy and fun to create these guides. https://ifixit.com/Guide/new The iFixit community will appreciate this.