Reclining Hero, or in sanskrit: Supta Virasana, is an intermediate pose and should not be attempted unless you can comfortably sit on your bum while in virasana – or hero.
Starting from your hands and knees, knees and feet spread wide enough so that your bum can fit between them, on your exhale, slowly shift back your weight and bring your bum to the floor. Sit with this for a few breaths.
Then slowly, using your hands then forearms, on your exhale, shift your weight further back yet until your fully reclining.
It is advised (and handy) to use a bolster to support your back in a semi-reclining state until you are comfortable and are looking for a deeper stretch. Use the bolster in such a way that it aligns with your spine and supports your full back, not just your lower back.
Now, it is also very important to learn how to get out of this pose. Slowly, with your forearms pressed against the ground, flex your shoulderblades and bring your chest upward, trying to avoid leading (thus straining) with your neck or head, until you are in virasana. From here you can once again roll onto your hands and knees to an ideal partner pose of a cat/cow combination to softly release that quadriceps tension.