Contact
Email hello@keepexport.com. Replies usually within a few days.
Reporting a conversion problem
Please do not send your whole export. Copy the single .json file of the note that converted badly (from the Takeout/Keep folder), remove anything private from it, and attach that together with the destination you chose.
Requesting a format
Say which app you are importing into and which file types its importer accepts; that is usually enough to add it.