iPhone 8 started glitching and cameras don't work

My iphone 8 was not in contact with water, but it suddenly started glitching and the cameras didnt work etc. You could also see water drops on the inside of the camera if you looked closely. So i put it in a bag of rice for 24h. Now it works fine, except the back camera which wont turn on at all, the volume buttons and speaker and some slight glitching when i use it. So I wanted to hard reset it in hope that it might fix some of the problems, but how do i do that with the volume buttons not working?? I have tried using the volume buttons on assistive touch but that didnt work...

[Re-Titled by Moderator]