First... Get your printer working well enough it can print a small object (Calibration cube???) in the center of the bed. Don't try to bring up UBL without being able to do this.
Once you can print a small object in the center of the bed with no issues... The G29 P1 should probe the entire bed working out from the starting location. It should not probe in the air. It kind of sounds like you have the Z-Probe endstop inverted???? You can check that with M119. It should report Open when in the air up above the bed and Triggered when you press and hold the switch.
Once you can print a small object in the center of the bed with no issues... The G29 P1 should probe the entire bed working out from the starting location. It should not probe in the air. It kind of sounds like you have the Z-Probe endstop inverted???? You can check that with M119. It should report Open when in the air up above the bed and Triggered when you press and hold the switch.