How can I fix a phone that is stuck in fastboot mode?

1. Check the manufacturer’s help page for instructions.
2. See if your phone can be booted into recovery mode by holding specific buttons during startup.
3. If there is an option to select reboot to fastboot mode, try that instead.
4. Flashing a new version of the OS on the device might also solve the problem.
5. If all else fails, try a factory reset. Do note that this will wipe all data from the device.