You cannot deactivate a plugin after it has been activated in your ServiceNow instance however you can edit the application menu and make the active to false so that the module won't show under the filter navigator.
You can enable (show) or disable (hide) an application menu or module in the application navigator.
Please make sure you are logged in as admin.
Customers at times want to be able to deactivate unused plugins, as per design, plugins cannot be deactivated but you can hide the functionality, please follow the instructions below.
1. Log into your instance as an admin
2. Navigate to System Definition > Application Menus
3. Click All in the breadcrumbs to display both active and inactive application menus (remove the default filter condition).
4. Click the desired title. The application menu record opens and the Modules related list shows the modules that appear in the application navigator.
5. Enable or disable the application menu and modules as desired
6. Click Update