I've just started using LNM with MS Flight Sim.  If I set up an A to B route with waypoints the autopilot works fine.  .

But if I set up a circular route to land at the airfield I took off at, the autopilot ignores the route and lands immediately.

How can I tell it to fly the route?

Thanks

Not sure if I understand but LNM does not do anything with the autopilot.
You can create circular routes or even plans with only one airfield and LNM will show the correct distances. Interpretation of this depends on simulator or aircraft add-on.

Sounds more like a problem with the aircraft GPS and/or the autopilot.

Alex