It’s possible to import relations from an XML file through the Settings > Custom Related Posts > Import Relations page.
Just make sure your XML file is in this format:
<relations> <relation from="32" to="34" both="true"/> <relation from="32" to="36" both="false"/> <relation from="36" to="34" both="false"/> </relations>
The post ID has to be used for the “from” and “to” attributes.