RICH
I was using Avenir Next Medium -font using title selection "expand" just select to edit title and at the end of the line just use cmd - RTN ( ie carriage return) and it gives a new line.
I have read that only certain title boxes or fonts can take this command, but not sure as I get into it more I will find out, I cannot find a list of what "title@ selections are applicable in iMovie
As I referenced : I guessed this as in microsoft- excel you use the same command to get a new line within a cell and it works
Hope this helps
Trevor