Honda HRS21 Owner's Manual page 12

Drive Clutch Lever (Self-propelled type)
To propel the mower, move the drive clutch lever forward against the
handlebar with one hand, while holding the flywheel brake lever against the
handlebar with the other hand. Both levers can be held against the
,handlebar with one hand while the mower is being operated.
Release the drive clutch lever to disengage the drive.
NOTE: If the flywheel brake lever is also released, the engine will stop.
CAUTION: The drive clutch lever must be released for starting, otherwise
the mower will move forward when the starter is pulled.
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