Leave the stroller set up in the house and let your dog explore it. Praise them when they go near or investigate it so that they understand that it is for them. Leave treats and toys in the carrying compartment and praise them if they get into it. If they need to be lifted or helped in them remember to praise and encourage as you do this. Do not force them to stay in there and work up to using the leash clips or restraints so your dog is comfortable with the space first. As with any new item you are introducing to your dog time and patience are the keys to success.