ANDROID STUDIO CANNOT RESOLVE SYMBOL ERROR

I started learning Android to support the mobile application of the company I work in recently.

I installed Android Studio and imported my company's project. But, as the libraries were not attached, all class names were red as in the photo.

HOW DID I FIX IT?

Click File tab on left corner of the page then Click Invalidate Cacehes / Restart... tab

It will restart Android Studio and the problem should have been fixed :)

HAVE A GREAT DAY Y'ALL :)