How do I Factory Reset a BQ Aquaris M10 tablet?

There's a timing play to successfully factory reset the BQ Aquaris M10 tablet

1. Start with the tablet powered off.

2. Press the power and volume up keys simultaneously

3. Release both keys immediately when the BQ logo appears.

4. Use the volume buttons to cursor down to wipe data/factory reset then press the power button to select it

5. Select Yes--delete all user data and press the Power button once

6. You'll now have the screen shown here, simply cursor to reboot system now with the volume buttons and select it with the power button. This should bring you back to factory condition.

If for some reason this doesn't work for you you should likely reflash the firmware.

Sources:

https://www.hardreset.info/devices/bq/bq-aquaris-m10-hd/hardreset/first-method/

Problem flashing Ubuntu Touch Firmware on Aquaris M10 (frieza)