Hi Trinetra,
Not very sure how have you configured your system. But in SPRO, Go to Governance Risk and compliance ->Access Control -> Maintain Business Processes and Subprocesses and maintain right subprocess under Business Process. PFB the screen shots.
For example, in the second screen shot, If I want to maintain SECURITY as one of the sub process under Basis, I should maintain SECURITY only under BS00 and not under any other Business Process.
In the request, If the user selects the Business Process as BS00(Basis), he/she will only be able to see SECURITY as subprocess and not anything else.
Hope this clarifies your doubt.
Regards,
Muhammad Fazil