After waiting, check the water level. If it has gone down slightly, that is a good sign. Try a test flush.

If the water level goes down on its own, flush the toilet. If it still drains slowly or not at all, repeat the process or try a plunger.

If the toilet bowl is filled to the brim and looks like it might overflow, and push the flapper down to stop water from entering the bowl. If the water level is low, you can skip this step.