Hello there @AbdulRehman-745 !
We may require more context for the issue you are dealing with. Yet, it sounds like you are working with City Sample as a base, since that’s where the Traffic plugin comes from. If this is the case, a similar scenario was encountered in the thread below:
In short, re-downloading the project should restore the missing plugin. Alternatively, you can check “C:\ProgramData\Epic\EpicGamesLauncher\VaultCache” for related files, the plugin could be present there. If so, restore it to its former location, and re-open your project.