Gardeo GMTBT50HP55BS Manual page 56

Do not adjust tilling
depth unless tine clutch
control lever is released
to the neutral position.
For heavy soil (100mm / 4" depth or greater),
remove the depth regulator rod and work the
tines down with a back and forth motion to at
least a depth of 100mm (4"). Slowly pull the
tiller backward allowing the soil to feed forward
over the tines.