Solved / Update; after performing a search on this same question but using Dell instead of ubuntu.
A solution was found. Placed DVD with ubuntu ISO on it, inside the CD/DVD drive, restart the machine, upon Dell logo appearing press F12 and you’ll be taken to a choice for booting by CD/DVD drive, select enter and DVD ISO will load.
It is a temporary operation that requires repeating anytime you want to load from DVD! But it works and you don’t have to get into BIOS and start changing things!
OP: I have a new Dell laptop, accessing BIOS is not a problem. When scrolling down to change boot order the highlight jumps right over the line to change boot order so that CD is first.
(ubuntu-MATE-18, Dell Inspirion 15 - 5000 series)