Um did you check the link I had posted?
((item 0 of it, name of item 1 of it, (id of item 0 of it, name of item 0 of it) of (fixlets of item 1 of it, item 0 of it) whose (mime field "x-fixlet-scm-id" of item 0 of it = item 1 of it)) of (unique values of mime fields "x-fixlet-scm-id" of fixlets of it, it) whose (multiplicity of item 0 of it != 1)) of bes custom sites
This Session Relevance should work in Web Reports, the BigFix Console Presentation Debugger, or via the API. It does not require that you've imported anything into Compliance yet. Is this not working for you? It should return the values for x-fixlet-scm-id, Site Name, Fixlet ID, and Fixlet Names for all of the duplicated x-fixlet-scm-id values in every Custom Site.
Once those are known, you do still have to export them from the console and edit the x-fixlet-scm-ids in the exported XML and re-import; or, more likely, you'll find you don't need the duplicates anyway and can just delete them (in my case, an operator had imported an entire checklist twice into the same custom site, and every fixlet was duplicated; I was able to just sort them by modification times and delete the older versions).