The belt needs to be connected with the tensioner loosened so that the tensioner can be used to take up any excess slack.
Tighten garage door belt.
The specific procedure should be in the manual for your unit.
This is a very simple job to do yourself in fact all you need to do is follow this simple 6 step guide.
All you need to get started is a step ladder a 7 16 inch wrench and a flat head screwdriver.
Loosen the adjuster three turns counterclockwise if the door raised without.
1 close the garage door.
The only thing you need to do with a belt driven opener is to adjust the belt occasionally.
In most cases all you have to do is adjust the opener belt of the belt drive tightening it to ensure smooth running.
The manual does not indicate how to solve this problem.
Step 1 closing the garage door before beginning use the garage door opener to close the door and fasten it.