Not sure which markers you are referring to. If you are generating in and out points, the subclip markers default to the in where the playhead sits and the out at the end of the clip. all you need to do is move to the location where you want the out point and hit the "O" key. You can also slide the out point to position with the mouse. There is a preference to create an outpoint of a marker when you set a new in-point if that will help.
Maybe a little more information about what you are trying to accomplish will help to arrive at a better answer.