You can use a towel or an old pillowcase. Try to pick something that you can take with you and that you don't leave on the floor normally
Use a treat to lure them. Eventually, they will just know what to do
The app will tell you exactly what to do while your dog calmly sits and waits on their mat
When your dog succeeds reward them with a treat and say 'Yes!'
On the second attempt break the task into smaller peices that your dog has a chance at succeeding at. If they fail twice just move on
Put that mat away and show your dog some love. Don't worry about tracking your progress, the app will save it for you
or read this blog post for extra details