LG G3 F400K Hard Reset Problem

So I was trying to mod my Camera. I followed a certain video which I thought was doing the steps right until I was able to read one of the comments. Unfortunately, after I rebooted my phone, it won't go further but the startup logo. I am a beginner in these kinds of things. How to do a hard-reset in LG G3 F400K? I have searched a lot of tutorials which are all similar but won't work with my phone.

Please halp :<