Replace the battery or buy the Apple Smart Battery Case here is a link to the website https://www.apple.com/au/shop/product/MG...-6-6s-smart-battery-case-white
step 1 undo the screw on the back Step 2 gently remove the hard drive (it is silver) Step 3 Unplug the cable from the hard drive Step 4 put new hard drive in a reconnect cable step5 put screw back in step 6 you're done