Here's a list of ballot boxes where you can take your completed ballot in person. You do have two options: they either have to be postmarked by election day or dropped into a ballot box by 8pm. Here's where you can find the closest ballot box near you!
I've seen that if you don't choose one of the two parties listed, Republican or Democrat, that they won't count your ballot. Weird. Also, make sure if you're choosing Democrat that you don't pick someone who has recently dropped out like Warren or Buttigieg.