Copying post_title to a wp_key in myPHPadmin

Not sure if this is possible or that this is the best place to ask, but worth a try, I am not very experienced with myPHPadmin, I have managed to change/update custom field names, but I would like to copy and/or duplicate the post_title of the custom post to a custom field value.

I have used the following (successfully) to replace a custom field name:

UPDATE "wp_postmeta"
SET "meta_key" = replace(meta_key, "OLD-CUSTOM-NAME", "NEW-CUSTOM-NAME"")

But I am not clear on how to copy the post_title from another table to replace a current available custom post value, does anybody know the code needed?

I hope that makes sense, thank you in advance!