hey tina. the battery on the iPhone 6 is covered by apple's extended warranty. for $29 they'll replace the battery for you. contact apple support online, plug your phone into your computer, and they'll do an online diagnostic. just tell them "it overheats." you mail it in, or take it in person to the el paso apple store. if you decide to go to ep, best to get to the store before it opens at 10. the line on the left at the front door is for technical support, and it usually takes about 1.5 hours to complete the repair.
getting the phone apart and back together can be tricky.