You have to open the debug menu in the downloaded build first. To bring up the debug menu:

• For computer users (Mac/PC), press the Tilde key “~”
• For mobile users (iOS/Android), hold your thumbs on the top right-hand corner and bottom left-hand corner of the screen at the same time

Once the debug menu is visible, you’ll see several hexagonal shapes. These are your menu options! They will look like this:

You only need to click Network.
In it, change those links:

Network → Island News → waddlepenguins.me/news

• Changes the Island News link to our blog.

Network → Web Services → Account → api.waddlepenguins.me/mix

• This will make you able to log in to your WPI Account and/or create one.

Network → Web Services → Game → api.waddlepenguins.me

• This will make you able to see your friends in-game.

Network → Web Services → Login Part 2 → api.waddlepenguins.me

• This makes you able to log in.

Network → Web Services → Login → api.waddlepenguins.me

• Makes you able to log in.

After you change those things, please click the X and restart the game.
Then click “Create an account”¹ and follow the instructions.
When you're finished, an error may show up. Ignore it and restart the game.
Log in and play with your friends online!