Zero out Altimeter on Iris+/Transmitter

Have a strange problem, when the Iris is on the ground, the altimeter reads -1m. Is there any way to “zero” that out?

Thanks for any help/info

If you plug in the battery on a table and then set it down on the ground, the barometer will read negative altitude. Make sure you leave it leveled while the pixhawk starts up. I also recommend you upgrade to newest firmware version of 3.2 in mission planner under beta firmwares, there were some improvements on barometer data.