How would you repair this?

Just wondering
It´s the traditional Martin, what they call; ivory top binding, but I´d say it´s genuine plastics, now isn´t it?
The binding is however coming loose.

Kind regards Henning

That generally comes from a rapid temperature change. The wood and the plastic expand and contract at different rates and pull apart. It can be fixed with the appropriate clamp and wood glue.

Over time the plastic shrinks and pulls away from the waist. Could be that, too. It usually takes some carefully applied heat to stretch it back in place. You could also snip it, file the ends square, glue it back it place, then splice in a piece to fill the gap. You might get a cleaner joint, though, if the ends were ramped and a longer splice glued in with airplane glue overlapping the ramps and dressed down. But its never easy to hide the glue joints in light colored plastic.

If properly shaped cauls can be used to force them back in place, great. But it has seldom worked for me.

Shrinking plastic- why i don't use the stuff.
As there is already finish issues on the binding lines, I would:
Snap or cut it.
Insert matching slice into gap- plastic binding can be melted/blobbed together pretty seamlessly.

I'm assuming it doesn't push back into place very easy (cuz it rarely does)

Is it a new instrument? I might see if the warrantee is still good.
Its easy to fix...but getting the cosmetic details right could be tricky. I would warm it slightly and clamp it back in place. Then apply a couple drops of thin CA glue (super glue) to the joint. It will wick in there and hold the plastic binding well.