Can't add modules to installed Unity editors

I've solved the issue by reinstalling the Unity Editor version I was using via the Unity Hub.

It seems that Unity Hub doesn't have the option to add modules to Unity Editor versions which have been installed using the Unity Installer instead of Unity Hub itself.

It is worth pointing out that Brian Choi's answer is a valid workaround, however I wanted to use the modules functionality of Unity Hub.

I got strait solution for this issue

No reinstall require. No redownload require. One click Restore all unity editors including Modules.

1. Remove Unity editor from the hub.
2. Go to Unity hub setting.
3. From General tab you will find the default editors path.
4. Locate the path and hit save.
5. Enjoy. :)

1. Press three dots
2. Remove from hub
3. Go to https://unity3d.com/get-unity/download/archive
4. Press unity installer
5. After this it will show message "You already have this unity version installed"
6. Now this Add modules option will appear.