Reference images can be transformed via the menu offered through a click of the RMB. Additionally, you have the few options the Tool Option-Docker offers.
As reference docker I know “Reference Docker” from Antoine Roux updated by @SchrodingerCat what can be found here:
Here you find the original one:
And I know “Reference Tabs” @freyalupen published last September here in the forum, which I find very capable: