Prop Hunt server voting


I’m running a prophunt server. I’m kinda a noob regarding Lua, but i need to know some things.
From my understanding, Prophunt is related to the Fretta gamemode.
Currently my server allows people to vote for gamemodes. The server asks for a gamemode change every 30 mins or so aswel.
I want to disable the option of gamemode changing on my server, for both automaticly and by votes.
I know there is a command to disable voting entirely, but I want people still be able to vote for maps.

How would I do this?

Thanks in advance for your replies.