I had one of the Raytheon
(Autohelm) RL9 which I suspect is similar.
After a lot of non use, the internal coin type battery
was bad which made it lose its original setup.
I soldered in a new one (not hard) and finally found the way to set it up.
Here's link to the manual which may be very similar to the one you have.
I suspect the procedure is the same.
It worked for me. See 3-10 and 3-17. Go to "setup page" and turn it on.
It's been ten years at least since I had that radar
, so memory's a bit vague, but I think that's where you can adjust the heading line and save it before you exit that menu. Good luck.