I had my quest plugged into my computer and I accidently unplugged it and the sidequest download got corrupted and dissapreared. I tried downloading it again via email but it game me an apk file and I dont know how to manually put that into my quest, please help

This guide will help you to install the apk file on your Quest : https://uploadvr.com/sideloading-quest-how-to/
Look for the "Sideloading an .apk from an external source" part in the bottom of the article.

I hope it helps