How do I reposition MidAirAnchor?

I position mid air anchor with the following code:

contentPositioningBehaviour.PositionContentAtMidAirAnchor(transform)

Since the AR object would stray away from the original position I anchored it after I walk around for a while, I would like to reposition the anchor whenever I look at the target image again.

But the result is not desirable when I use the same code to reposition the anchor(sometimes it is a success but sometimes the ar object isn't positioned properly). Maybe this is because the old anchors are affecting the anchoring. So maybe I need to remove the old anchors first.

What code should I use to remove the old anchor? Or is there a better way to do this?