By default, the <dbname> is test but to create your own dbname, you need to change the <dbname> to the name of database you’re interested to use. MongoDB Atlas will automatically create the db for you based on the name.
For example: Creating a db for Qlabs with username=Que and password=pin123
mongodb+srv://Que:pin123@cluster0.pfose.mongodb.net/Qlabs?retryWrites=true&w=majority