Open the tape deck covers. If it is possible to take the covers off, do so.
Coat one end of the cotton swab with the isopropryl alcohol. You don't want the cotton to be dowsed in alcohol, but you want to make sure to have enough the alcohol to clean the heads.
Rub the cotton swab on the recording and the playback heads in the player. This is what the tape runs across when it is playing. Also, be sure to rub the swab on the small rubber wheel which helps the tape move over the playback head. The cotton of the swab should be light gray when the cleaning is complete.
Reattach the tape cover. Place a tape demagnetizer in the tape deck and demagnetize the heads. The demagnetizer looks like a cassette tape. Be sure to follow the instructions on the demagnetizer.
Let the equipment wiped down with the alcohol to dry. Once the tape deck is cleaned, play a tape to test.