Resistance Is Not Working on My Bike.

Anytime you have a resistance problem on the bike, you need to try to use the app on another device to see if the issue persists. If it does, then the culprit is most likely either the resistance module or the encoder wheel of the bike.
If you have an EX1 or EX3, then check the wires going into the console of the bike.
Unplug the bike, unplug the wires going into the bottom of the console, and plug them all back in.
Check the serial number to determine which tablet you have. GloryStar tablets will have GS in the serial number, and Kinstone tablets will have KS in the serial number.
Clear the Bluetooth cache by referencing the articles here:
How to Clear Bluetooth Cache on the EX-5s or Solve "Bluetooth Share Stopped" Issue (GloryStar)
or here:
How to Clear Bluetooth Cache on Kinstone Mounted Tablet
Then, check the resistance again. If you are still having the issue, then the encoder wheel will need to be replaced.