You may set your default location by following the below steps:
Navigate to the the dashboard or forecast page.
Click on the location drop down.
Click on the heart icon next to the location that you want to set as default.
From now on, this location will be your default location.
Tip: You may also select the pin icon if you have multiple locations. This will allow you to navigate to that location quicker as it will be pinned to the top of the list. To unpin, simply click on the pin icon again.