Kelu cannot index past Front conversations as a knowledge source. The ticket source under Add source reads Zendesk only. Here is what you can do with Front:

Answer incoming conversations

Click Connect Front and approve as a Front admin, in the same browser. If someone else is the Front admin, add them to this Kelu workspace as an admin and have them click Connect Front. Conversations reach Kelu automatically, and it answers, drafts or tags the ones in the Front inboxes you pick, from your knowledge base.

Index your help articles

If your help center is public, add it as a Website source.