If you'd like your online store to show on your own domain at checkout (instead of *.RentMy.co), then you need to edit the following DNS settings with your registrar:
The inputs with your domain registrar are:
The hostname is your hostname and '@' means the primary domain
Keep in mind:
If you are not certain how to handle this change, you should contact your domain provider to find out how any changes might affect your DNS settings.