How does one set the PITCH of Fixed Wing to LEVEL while on the bench?

I have a PX4/Pixhawk in a FIXED WING.
I am using Mission Planner …
I need to SET Level (Pitch & Roll) AFTER the AutoPilot has been placed in the Plane (with the plane on the bench and PITCH and ROLL of the plane truly level.
How do I do this?

Although the AutoPilot was ‘leveled’ on the bench outside of the plane by a previous individual, I now need to ‘tell’ the AUTOPILOT what the LEVEL is when the plane is LEVELED on the Bench (Pitch and Roll).

In Mission Planner -> Initial Setup -> Accel Calibration there is a button “Calibrate Level”. Does this do what you want?

It did on a fixed wing I am using a mRobotics x2.1 v2 controller in. It didn’t in a fixed wing I have a APM 2.6 mounted in.

APM 2.6 is outdated hardware and no longer supported. (See the note here: So I am not sure if it supports the “Calibrate Level” functionality or not. Per the note, if you choose to use the APM 2.6, make sure you’re using Plane 3.3.0 or older.