Ubiquiti PowerBeam M PBE-M2-400 Quick Start Manual page 7

3. Push in the sides of the Cable Door and detach it from the
Rear Housing.
4. Attach the Antenna Feed:
a. I nsert the Antenna Feed into the Rear Housing, and push
until it locks into place with a click.
b. Lightly pull the Antenna Feed to ensure that it is locked
into place and the Release button is fully engaged.
Release Button
Bottom View