Parivrtta Janu Sirsasana is a modified Head on Knee pose (just Janu (knee) Sirsasana (head)), being Revolved Head on Knee pose, so feel comfortable setting yourself into that pose, too.
To start this pose be seated with your legs straight out. With an inhale, bring your right knee upwards and tuck your foot in close to your left thigh as you draw your right heel towards your root chakra.
With an exhale, shift your torso so your bellybutton is facing straight out, parallel to the floor and your right thigh. Hold this for an inhale.
With your next exhale, slowly bring your left hand down towards your left ankle and your right hand towards the sky. With your inhale, focus on straightening your spine by keeping the bend at the hip.