That model Briggs & Stratton engine does not have a drain plug. The manual suggests draining the fuel before tipping the engine on its side to remove the oil through the fill area.
Change oil while engine is still warm from running,as
1. Drain fuel tank by running pressure washer until fuel
tank is empty.
2. Disconnect spark plug wire and keep it away from spark
3. Clean area around oil fill, remove oil fill cap/dipstick.
Wipe dipstick clean.
4. Tip your pressure washer to drain oil from oil fill into a
suitable container making sure you tip your unit away
from spark plug. When crankcase is empty, return
pressure washer to upright position.
5. Slowly pour recommended oil (about 20 oz. (0.6 I)) into
oil fill opening. Pause to permit oil to settle. Fill to Full
mark (top hole) on dipstick.
6. Wipe dipstick clean each time oil level is checked. DO
7. Replace and tighten dipstick.
8. Wipe up any remaining oil.
9. Reconnect spark plug wire to spark plug
This is copied from the owners information manual.