Remove the screws securing the servo arm/wheels and pop the arms off the servo's shafts.

Now power up your transmitter then your receiver. The servos should all centre temselves, except of course, for your throttle servo which will go wherever you have the throttle set!

Make sure you have all the trims for your control surfaces centred.

Now put the servo arms back onto the servos with the arms at 90 degrees to the servo case. Don't put the screws back in yet.

Adjust the clevises at the control surface so that the ailerons/rudder/elevator is in the neutral position.

Double check everything and put the servo screws back in .

Fly and fine tune as necessary!