Can I roll back a changeset in Collaborator?

A user accidentally added a changeset to a review and wants to remove it. The Delete button is not available for that changeset. His comment:

"This tool clearly has use scenarios not fully supported. GUI client interaction with git can easily result in contamination of changelist, yet, there is no way to "confirm" or undo the upload. Even if rollback is not available, there should at least be a detailed capture of history showing all actions of participants (similar to what Polarion does)."

Any comments?