I recently obtained a Yaesu FTDX-400. I have operation and
service manuals but I can't find how to add bands.

--
There is something outrageous about such a huge body of evidence being
put together, then being confirmed in all kinds of other scientific
disciplines, particularly genetics, and having other people just sort
of deny it for reasons that have nothing to do with truth.
– Matthew Chapman, Darwin's great-great-grandson.