Use the hose attachment of a vacuum cleaner or shop vac to clean in and around the hole at the back of the dryer.
Clean dryer duct in wall.
In the photo above the back of the dryer is on the right and the wall bent on the left.
Brush kits come with a long bristle brush to clean the lint filter area as well as a round bristled brush that can clean out a 4 inch round rigid dryer duct the kind you should have for all concealed portions of your duct run.
Cleaning lint from a dryer duct requires a vacuum.
I personally replaced the original semi rigid venting with a pair of 90 degree.
Your goal is to attach one straight side of the tee to the wall or floor vent and one to the dryer outlet.
Remove and vacuum the hose.
Reattach the hose and clean the exterior vent.
The round brush tip fastens to a flexible fiberglass shaft that can be lengthened in sections.
The tools and supplies you need to clean a dryer vent duct include a vacuum with a long hose attachment dryer vent brush kit screwdrivers and ul listed metal foil duct tape.
If your dryer used a soft foil style vent to link to the wall duct get rid of it.
Now you are going to pull your dryer away from the wall enough to get in there behind it.
Detach the dryer vent hose from the wall.
These hoses are a known fire risk.
It will make cleaning it easier.
If you can detach the length of duct where it meets the wall do so.