From page 46 of your operators manual for BX23S:
Stationary PTO
To park the tractor and use the PTO system (for chipper
or pump, for example), start the PTO system in the
following steps.
1. Apply the parking brake and place blocks at the tires.
2. Make sure all shift levers are at "NEUTRAL", and start
the engine.
3. Set the PTO clutch lever to engage "ON".
4. Set the engine speed to provide recommended rear
PTO speed.
5. Unlock the seat lock lever and stand up and raise the
seat.