How long have you had them? They probably just need time to adjust. If they are retired laying hens I'm sure they need a break, and are scared of this big new world that is suddenly available to them. Give them time and patience.
They've been life that their entire life getting them to change will be hard, I would take each one out 1 by 1 and put them in the grass and grab a handful put in front of their beak and see if they will peck it to try it.
We have had them a week. I take the outside and before I can go back to get another one that one has already ran back inside. I hate to lock them out bc the one egg they did lay was not in the nest and it was during the day. I don't want them to start laying eggs outside.
I would buy some mealworms and bring one outside and give it the worms. Do this for a few days for each one and then try throwing some on the ground and see if they come out. They probably just need some time. Good luck!