Hello Kamal,
here my standard answer to this topic:
generally we do not recommend hiding/disabling Previous and Next button of the GUIDED activity floorplan (GAF), because those are the basic buttons to navigate through the scenario.
What you would like to have is a possibility which hinders the user navigating to a further step. You can do that by setting the navigation event FPM_NEXT_STEP and setting it - under a certain condition - to value FAILED. You do this within PROCESS_EVENT of your UIBB component or AppCC, setting exporting parameter EV_RESULT = 'FAILED'.
To show the user the failure of the event, additionaly you could raise an FPM error message - inside there you could also mention the reason why navigation has stopped.
Best regards,
Julia Bender