I have a self propelled

Question

I have a self propelled Royal Dirt Devil vacuum model number 087900 and it goes backward fine but forward has to be pushed so hard it's impossible. Is this a switch? Do you know about how much the part would cost and can it be done by a beginner. We fix a lot of things ourselves but we aren't mechanics by no means. We put a brand new belt on it. I don't think it can be put on backwards and brush turns fine. Where is the switch? Use layman's terms.