Turn off the dryer and turn off the electricity to the dryer. This will prevent shock injury for both you and the squirrel.
Check the vent opening on the exterior wall to make sure it is completely open. Remove any obstruction that may inhibit the squirrel from leaving the vent.
Check to see if the squirrel is in the hose. If it is, use your hand to push it back into the wall Disconnect the vent hose from the dryer and not the wall.
This will inhibit the squirrel from falling out of the wall and into the house.
Thread a broom handle quickly through the dryer vent hose to push the squirrel back through the wall and outside. A broom handle should be long enough to reach the outside end of most vent hoses.
Reconnect the dryer vent hose. Install hardware cloth on the vent opening to prevent squirrels from entering the opening again.