AHRS_TRIM or SERVO_AUTO_TRIM=1

Hello. I am newbie to airplanes. I use pixracer in dart250g airplane and have bad experience with launching by hand.
I read documentation and found two trimming procedures. First is leveling FC. Second - “leveling” elevons. Which is better and enough?
I assume that FC is set at an angle of 2-3 degrees relative to the horizon.

Is it enough to simply turn on the SERVO_AUTO_TRIM=1 and trim the elevons to compensate for the uneven FC setup?

Or i must leveling FC before? But what can be considered a horizontal plane in an airplane?