Hi mlanyi,
Welcome to the Heartland Owners Forum.
Thetford toilets are a split construction. Assuming there's no damage to the parts that seal the two halves together, you can tighten the screws from the bottom. The toilet has to be removed to do so.
If this is a new trailer, you might want to call Heartland Customer Service at 877-262-8032 / 574-262-8030. Have your VIN # ready. They might just send a new toilet for self install -which is pretty easy.
If you have a Dometic/Sealand toilet, I don't know that they're built the same way. If one of those is separating, you might need a new toilet.