Indra Puranmashi falls on Purnima in Bhadrapada Month as per Hindu calendar. In 2017, Indra Puranmashi date is September 6.
On this day the Vrat begins with Upavaas. The performers wake up in the early morning and have bath. Wear satvik clothes and start the upvaas by praying to Indra deva.
During this vrata, the performer should felicitate his wife by adoring the jewellery. This gives Moksha (salvation).
There is no much information available on Indra Puranmashi Vrat. But it is mentioned in Hemadri Vratakhand.