Hi Suvrat,
To switch between the subsystem based on some condition, you could use "IF- Block" and "If Action Subsystem".
Please refer to the below documentations of both the blocks to understand how to define the condition in "If Block" and how to switch between the subsystems.
IF Action Subsystem documentation : https://www.mathworks.com/help/simulink/slref/ifactionsubsystem.html
I would suggest to use "MATLAB function block" in case of "IF-Block", if the conditions that needs to be checked are complex.
