While I tried to run the flutter doctor command, I got an error "Flutter plugin not installed error;. When running flutter doctor". I got this problem solved by following the below steps.

Steps to Resolve The Problem:
  1. Open Android Studio.
  2. Go to The File Section.
  3. Click on the "Settings".
  4. Now click on the "Plugins".
  5. Search for "flutter" on the Search box.
  6. Install the "Flutter" Plugin.
  7. You are done.

I hope your problem is solved now.

Thank you.