you cannot repair, reconfigure or create new pair from Site A -> Site B and vice versa, because sites are not in sync. For example, if you have a Protection group and Recovery plan you will have information for this only in Site A, but Site B will be with clean DB and this information is missing. A possible solution in your case is to Uninstall Site A SRM with delete SRM data and install it again. After that, both sites will be with clean DB and configuration and it's possible to pair sites.
Hope this helps,