Massallah pertaining to Safs

Assalaamu’alaikum mufti sahib, what is the way in which you move somebody back to start a new saf during a jam’aat. do you start your own prayer and then step forward and place your hand on a person’s shoulder to indicate to them to move back, or do you move somebody back first then start your own prayer. Also do you move somebody back from the sides of a saf or from the middle.
Jazaakallah khair.