If you want to connect your Mac to a different WiFi network that is not installed by default, you will need to change the order of the networks you want to connect to. Here's how to do it.
Step 1. Open System Preferences
You can do this by clicking on the Mac icon in the top left corner and scrolling down to System Preferences.
Step 2. Select Network
Step 3. Make sure WiFi is highlighted on the left, then select Advanced
Step 4. Browse the list of preferred networks and find the WiFi name that you want to make the default network
Drag it to the top of the list. Click OK. Then, if asked to confirm the changes, do so. If the network names are gray and unclickable, go back to the previous screen and press the lock to allow changes.