If the cassette housing assembles with screws (typically 5 screws), you're in luck. If it's sealed, you're going to have to destroy the housing to get it apart. In either case you will need to have a new blank cassette in hand as you will simply be changing the housing or shell by putting the old tape in the new housing. Find a cassette that has a 5 screw housing or purchase a new tape to put your old tape into.
Remove the tape spools from the new housing and replace with the old tape spools (be sure to put the left one on the left and the right one on the right. Put the housing back together and you are good to go.
We recommend having the audio cassette converted to digital format if so it can be easily put onto a CD or mp3 player for long term archive purposes.
Let us know if we can help with the repair and conversion from cassette tape to digital format such as CD or mp3.