My install kit did not come with an iOpener. Do I have to buy one?

What it did come with is tweezers and a spudger im sure.

Use this guide to get the battery out: iPhone 7 Plus Akku tauschen

Loosening the adhesive under the bottom is only going to make it more want to snap more. If you would like to try it without the I opener, use a hairdryer. It works just as well as the iopener or heat gun. Also if the adhesive breaks. Go under the battery with the spudger on the flat side not the point side. Be very carful to not puncture the battery and work your Spudger up the battery. Another way to get it out is to Lift the battery a little and grab the white adhesive with the tweezers and spin the adhesive around the tweezers and pull the rest out to finish the job. I hope this helps.

That’s great, but 1) the instructions on the page specifically state use the iOpener, and there are other less expensive options out there that also do not have an “iOpener”.