Return on GW2
You can’t reset your progress on a character that’s progress through the initial story. You also can’t really reset your achievements either. However, Living Stories and the Heart of Thrones story allow you to re-visit the story chapters.
The only true way to erase any progress would be to delete all characters and start from scratch with new ones, but as I said, any achievement points you’ve already earned will still be there. Don’t forget though, you’ll lose any birthday gifts you’ve earned if you do that, so I recommend just make a new character and start from there, keeping your old ones for birthdays.
Welcome back to Guild Wars 2 though.
If you want to be extreme, start a Free-to-Play account. See if that brings back the enthusiasm… or if it reminds you of why you left… or if it reminds you that what you liked still allows you to play your original account.