Are you copying the incinerator from one of the official levels(like the guide suggests), or are you adding just the incinerator actor?

If you're copying it, you also need to select the green wireframe-box inside the incinerator, that's the trigger volume. It can sometimes be hard to see.

When adding the incinerator actor as is, it doesn't come with a trigger volume. That's why copying one from another level is easier for beginners.

I'm just adding the actor.

I can't seem to find any of the in game maps in the files to copy one from, so how can I add a trigger volume?

Edit: Could you link me to the guide? Please and thank you

The maps are located in the \Viscera\UDKGame\Content\Viscera\Maps folder.
The guide is here https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=323918819

Thanks, also, how to create geometry? Every time I try, I just get a wireframe box, and no matter what I press, I can't make it solid. I try pressing enter, nope. "Build geometry", nope. Then I do "Build everything", no dice.

Edit: Never mind, just found out how. Thanks for posting the guide though!