There is no need to do anything. When you insert a subVI into a main, execution will automatically return to main when the subVI finishes. If it's not, then is the subVI in some infinite loop and you're stopping with the "Stop sign" on the toolbar? Or, in your main VI, do you have a while loop so that it keeps running? Posting your VI and subVI would go a long way in pinpointing your error. Please do a Save With Options and save into a distribution llb so that all of your code is in one place. Since this is a pretty basic task in LabVIEW, you might want to check into some of the learning resources
here.