How to root LG K7 (MS330)?
I'm suggesting something similar to what @Gokul NC has suggested. I'm assuming you have a computer, so this is a better option with a higher chance of successfully rooting.

Access your computer, go to the browser, and download Kingo root from https://www.kingoapp.com. Once it's downloaded, install the program, connect your device, and you'll be given further instructions within the app. 
I have tested this method more than 10 times, you should experience satisfying results.