I stepped on a onewheel first time ever in July '19. Rode in my yard for 3 days slowly, total of 8 miles. Took it on the street the 4th day. It was so much harder to ride in the grass and it prepared me for the street.
With that said my suggestion is ride in the yard, flat mowed grass if possible for a couple days. When you get back to the street it will seem like a breeze. Go slow and let your brain/body adapt to what your doing. Plus when you fall it's much easier on your board and body. Have fun.