Begin by entering the preferences and scrolling down to the Editable Card Sets section.

Toggle Seaside to On.  This will allow you to edit the Seaside deck.

Go back to the main menu and View Card Sets.

Tap the Edit button in the upper right.

Tap Seaside to enter the editing view for the set.

Scroll down until you find Haven and tap it to edit.

Tap the 2 to change the card cost.

Now tap Done to save the changes.

Haven is now updated to its proper cost of 2.