If you are editing your tree online in a family site and make any change to your family tree, this should send a request to process Smart Matches on your tree.
If you are working in Family Tree Builder, then every time you sync (publish) your family tree, a request to process Smart Matches on your tree is sent to our servers.
Please keep in mind, that after a Smart Matching request is made, you will not get matches immediately. It takes time to process trees for Smart Matching.
Premium users get priority Smart Match processing. To upgrade your family site, please see: How do I upgrade my family site subscription?