How do you put a double hung window sash back in after removing it?

To reinstall a double-hung window sash, start by tilting the top of the sash inward and aligning it with the window frame. Carefully lower the sash into the frame, ensuring the side rails fit into the vertical tracks. Once in place, tilt the bottom of the sash up and push it down until it locks securely into the bottom track. Finally, check that the sash operates smoothly before securing any stops or trim.