Main panel

Select one or more clips and click on one of 9 positions in Anchor panel.

Anchor will keep original animation of a clip.

Use alpha channel

Enable it, to use clip's alpha channel for anchor position.

Use "Transform" effect

Enable it, to move an anchor point of Transform effect, instead of Motion effect.

If there is no Transfrom effect on a selected clip, it will be applied and then an anchor point will be repositioned.