mLab is a fully managed cloud database service that hosts MongoDB databases. mLab runs on cloud providers Amazon, Google, and Microsoft Azure, and has partnered with platform-as-a-service providers.
Connect with mLab mongoDB from Database Browser
Then in the Database Browser add-on, to make connection -
Select Database Type as "mLab - MongoDb"
Provide API that you got it from mLab
Press "Apply" button as shown in the picture
If you see any error, please check your API key