Hii!
You haven't mentioned the name of the course you wish to pursue on the College mentioned above.
The St. Mary's College, Shillong hasn't specified any official dates for the admission process to start for the session 2020-2021.
There may be a delay due to the Covid-19 pandemic. So, just keep a check on the official Website for updates.
http://www.smcs.ac.in/
Hope this helps.
Good luck!