Manually Assign State Entity to Switch

Hi everyone,

New HA user here. Been having a great time making the ol’ home smarter.

Just one thing I can’t seem to figure out. If 'n have a switch, lets say to open & close my garage door. Said switch does not have a state sensor (eg. reed switch), but my alarm system has a reed switch on the garage door. I have already connected the alarm system with HA and can see all sensors etc.

Is there a way that I can assign the garage door reed switch from the alarm to my garage door opener, to be used as the state sensor?

Thank you in advance