You can go to Preferences -> Build, Execution, Deployment -> Build Tools -> Maven -> Importing and check the box that says Import Maven projects automatically.
In Mac, you can do Command + Shift + A, then enter the action reimport, then click on Reimport all Maven projects.
You can go to Preferences -> Build, Execution, Deployment -> Build Tools -> Maven -> Importing and check the box that says Import Maven projects automatically.
In Mac, you can do Command + Shift + A, then enter the action reimport, then click on Reimport all Maven projects.
As mentioned by @maheeka in the question's comments, if the project is a Maven project, the simplest way to achieve updating changed external libraries is to right-click on the project, and select Maven > Reload project.
You can actually see IntelliJ re-indexing the changed libraries individually during the operation in the bottom right status bar.
Tested on v2021.1 Ultimate.