There are two Phillips #00 screws holding the battery connector bracket. You need to remove them.

One 2.2mm screw

One 3.2mm screw

Separate the metal battery connector bracket from the iPhone.

Gently pry up on the battery connector, and lift it out of its socket on the logic board. Use a plastic opening tool to do this.

Make sure to pry up only the battery connector, and not the socket on the logic board. If you pry up on the socket, you may break the connector.