go to the playlist node
select the all accessible files playlist
when it shows in the listview area, go to the menu bar and click on edit. then click on select all.
now you can click on find missing files and it should look for all of them., should but that is going to take
time if you have large library it might also crash the computer if you don't have a fast enough cpu or have
so it is always a good idea to select small groups of the songs to start and slowly add a few to the next group
until you see monkey start to slow down too much then you know you've put too much in that last group.