important! Deleting/purging items from Credo removes them from Fedora and the Solr search engine. It does not remove the original files from the server.
To delete/purge items from Credo, add a file to the /fedora/upload/purge folder with item PID you want to purge and no file extension. Like ingest, the purge folder processes every hour but will only purge 30 items per hour.
The advanced search collection autocomplete is populated by the OAI-PMH set list, which should have a list of all the collections in Credo. For a variety of unfortunate reasons not worth going into here, the autocomplete can't pull directly from the OAI-PMH endpoint. As a result, you need to download that file following the instructions on the adding collections page, then upload to Credo in /var/www/html/data, renaming it to oai.xml.
This should automatically update the dropdown.