You should be able to do it. I never have done this personally, but option was present in GoIbibo, IndiGo's own platform should also allow for this as well. If not then perhaps call CS and ask them to do it.
One time I was trying to reschedule few years back, price of rescheduling was same as cancelling. So I chose to cancel 😛
Rescheduling helps only when you have booked the ticket using some promo code which is not available to you now.
Don't know the present scenario but I feel it should be something similar.