The vent tube may be blocked
There is a corrugated white pipe that blows the warm air out of the tumble dryer. Check this has not got restricted by pulling the machine out and inspecting this pipe. Also disconnect it and look inside to see if it has become blocked with fluff. It may have a cover outside your property, make sure this has not been blocked. Any restrictions in the venting pipe will prevent your machine working efficiently
The vent hose is connected at the rear of the machine.
there may be a flap or grill as in the picture below, check that it is not clogged with fluff or that any draught flaps have not been restricted