For a workaround:
1. Solder any same size pot with suitable long wires to the location (if possible)
2. Adjust the brightness to Your liking
3. Remove the pot
4. Measure the resistance
5. Solder a measured value resistor where the pot was.
This way You get a fixed brightness and somewhat working computer.
Now You can wait for a replacement pot and play with the computer.
BR Matti