Ok, thanks for the replies. I do have a column in Calibre that I check when read, but I sort of like the new tags on books I haven't yet read on the reader. I was just hoping for an easy way to do it for the second reader and
as I typed that out, it dawned on me that I could have transferred over a file from the first reader to the second reader that contained all the read tags.
Well, I'll remember this for next time if I ever get a third PRS-350.