Hii Muskan!
If you specify the place of location of St Xavier's College you are askig about it would be better for us to answer the query.
Tentatively the application forms will be released in the month of May, 2020. The application forms are not released yet. The dates may vary as per the different courses. The entrance examination dates may also vary. So, keep an eye on the official Website for updates.
The link given below may help you with more information-
https://www.careers360.com/exams/st-xaviers-college-entrance-test
Hope this helps.
Good luck!