Here are some photos that show some of the details for replacing an upper meeting rail.
The original meeting rail has sagged about a quarter inch.
Use a plug cutter to access the recessed pins. You might have to remove a portion on the zinc strip to locate them. Remove the pins with a pair of pliers and pull the old rail away from the stiles.
Test fit the new meeting rail to the sash and mark the tenons on the end of any muntins. Then chisel out mortises for the muntins.
New meeting rail successfully installed.