I think location of cabin filter in Wingroad and AD Van must be same. If yes, then u will have to open the dash panels on lower left side of dash board (i.e. in front of second seater). It is not that difficult to open those panels. Just a 5-10 minute job, only few screws have to be unscrewed.
After opening the panels, u can locate the cabin filter around middle of the dash board extreme front portion. It will be difficult to find though.
I suggest that u take ur vehicle to different AC workshops and get it opened. I got it opened and cleaned in Rs. 100 few weeks back.