There are a few different ways of mapping data to that format, most importantly you can supply both a Taxon and a Name table/file. However, it is also possibly to use the NameUsage table/file to accommodate both accepted taxa and synonyms. I find the latter easier in most cases.
So my recommendation would be to map SeqCode data to
Once you have a zip archive, place it at some accessible URL from where it can be crawled/indexed by Checklistbank. You can log in to https://www.checklistbank.org/ with a GBIF user account. Once you have a GBIF username, we can give you an editor role, allowing you to trigger imports, change metadata etc.
Implementation details from Thomas Stjernegaard Jeppesen: