Admin author not showing up in author list

In 2011, I changed my site from one full of .shtml pages to one in WordPress. I’ve got a ton of pages on the old version of the site which I thought would be a good idea to import them into the WordPress site.

Not so, because (a) it created a load of duplicates, which I think I’ve now eradicated, and (b) I tried to keep them separate while I waded through them, so labelled the author as ‘Dom Robinson 2’.

Now, as I’m trying to sort out the pages I want to keep, I find I can’t change the author on those to ‘Dom Robinson’ because I am the admin.

Is there a way to resolve this, please? (preferably without complex coding within WordPress)

[Moderator Note: No bumping. If it’s that urgent, consider hiring someone.]