When calibration directs to "reboot" the aircraft, does it mean to turn power off then back on or completely remove battery & restart?
I "turned off" the aircraft and restarted but continued to direct to "reboot".....what up with that?

Rebooting the AC would be to turn off the AC, wait a few seconds, and then to turn it on again.  You don't need to take the battery out because turning off the battery cuts power to the battery contacts - unless something is seriously wrong with your battery.

Not sure what you mean by "calibration."  Compass?  IMU?  Gimbal?  RC?