There are two files called "persistent" that download together with the game. They essentially make it so the game thinks it's already finished. So achievements will be locked, the gallery will be unlocked and skipping will always skip unseen text.

The two files can be found at "steamapps\common\Heart of the Woods\game\saves" and "Users\YourUsername\AppData\Roaming\RenPy\hotw-02152019". Then delete them. You will know you did it right if the game asks you to set accessibility options before getting to the main menu.

I hope this guide helps!

Note: Due to the recent update this Guide is out of date and will likely not work