Lie down on the ground with your right foot on the corner of a wall or door frame to stretch out the left piriform muscle. Start with your right knee at 90 degrees.
If you are really tight at the beginning then increase the angle of that right knee by moving further away from the wall or door frame.
Cross your left ankle across your right knee and ensure that your buttock remain touching the ground firmly and your hips staying square to your body.
Stabilize your right ankle with your right hand and extend that ankle into dorsiflexion upwards. Then push your left knee towards your other foot while you keep your inner core engaged and your pelvis nice and stable. Hold this for 30 seconds, doing 3 sets on the affected side daily.
When you have sacroiliac joint pain and dysfunction, this exercise can help to relieve it.