Ok, so you switch the fuel Valve back to "Run" and then rotate the starter switch for the engine on the Overhead to "Start". Check if your engine has enough air to be started. If not, you have to start the APU and use the APU bleed. You also need to be on an altitude that allows in-flight engine start, which is considerably lower than your cruising alt! The FL depends on the engine type. If you successfully restarted the engine, check if there is any fuel imbalance because of the missing consumer. If there is an imbalance, follow the "fuel balancing" checklist. And if you can't restart it, find the next adequate airport for an emergency landing!! Good luck!!