How to fix a stuck automatic gearbox in an Audi 80?

I recently encountered a problem where my Audi 80's automatic transmission became stuck and would not shift gears. This has happened before and I had to get it fixed at a mechanic, but I would like to try and fix it myself this time. Is there anything I can do to fix a stuck automatic gearbox in an Audi 80?

First, check the fluid level and condition in your transmission. Low or dirty transmission fluid can cause the gears to stick. If necessary, top up the fluid or do a complete flush. If this does not solve the issue, it could be a problem with the shift solenoids or torque converter.