Reply To: I don't know what's the name for this kind of menu bar to find help about it.

[webinuse]

https://css-tricks.com/forums/topic/wordpress-custom-menu-3/
here is a thread from forum that was active few days ago, so you can read it and see if there is something for you.
https://www.w3schools.com/howto/howto_js_sidenav.asp
here is a tutorial with code and everything for creating a side menu, you just tweak two-three lines of code.
And also you can try to find your theme inWP repository, or you can buy a premium theme and have it fixed in matter of seconds.