As long as they know where the food, water, and shelter is, they will be fine. Just open the door to the run. They probably won't go very far for the first couple days. They might not even leave the run on the first day. Be around to monitor how far they get, though. When you want them back in the run calmly herd them back in. I stick helps to gently guide them.
You can also check out the article featured on the home page, "Deciding to free range your flock" by CarolJ. There are some interesting tips and suggestions listed inside.
The article can be found with the following link: https://www.backyardchickens.com/a/deciding-to-free-range-your-flock