Setting a new retarget source on persona

I honestly cannot change my current retarget source on animation retarget manager.

I had previously retargeted for a skeleton - It happens that other retargets I try to do use the one skeleton I had set as the source mesh. I want to change that - I want to kind of reset the retarget manager to start retargeting from a new skeletal mesh.

But welp, I don’t know how to do that - maybe am missing something simple ? Any pointers ?