Write down the make and model number of your cassette deck, which should be printed on the back panel. Purchase a replacement belt from your local electronic store using this information.
Unplug your tape deck. Use a screwdriver to remove the screws from the outer casing of your cassette deck and lift off the cover.
Look for the black rubber drive belt, which should be located near the front of the machine. Remember, or write down, the path of the belt around the different component in the player. You will need to position the replacement belt in the same way.
Remove the old belt by gently stretching it away from the components of the tape deck and lifting it off. Alternatively, if the belt is broken or stuck, use a pair of tweezers to avoid touching any other parts of the deck.
Install the replacement belt, making sure that it fits round the cogs and wheels in the same manner as the old one. Make sure the belt sits in the outer grooves of the wheels.
Plug your cassette player back in and press "Play" to make sure that the right-hand cog is moving counter-clockwise. Press "Stop" then "Rewind" to make sure that the left-hand cog rotates clockwise. Unplug your cassette deck if this is correct, re-position the outer casing and, using a screwdriver, replace the screws.