You may get Mock Tests online on Platforms like Toppr especially for VIT and BITSAT. Otherwise, what I suggest is focus strongly on JEE Main Preparation as well as BITSAT, before Exams of Private Universities, just get acquainted with the Paper Pattern, Test Strategy and few Mock Tests, and youll be good to go.

For more information about JEE Main Preparation do follow the link below

https://engineering.careers360.com/articles/jee-main-preparation-tips