How to make a document searchable without calling reindex search backend

I am unable to search a document by uuid. I would like to make it searchable. I think the usual way for it is to do the reindex search backend. I would like to do it just for this document. Not for all. How do we do that?

Is there a guide on how to increase worker count? I would like multiple workers on the reindex search backend task. Will the newly created documents be added to search while reindexing is ongoing?