I think the instruction is to right click on the library file which shows you the package contents so that you can follow the instructions there.
This has just happened to me setting up a new install (due self inflicted unrelated comp problem), but because I hadn't downloaded much at that stage I did the alternative of just deleting the whole library and letting it download a fresh copy, which is much more starightforward.
Deleting it is usually simplest if all your images are already in the cloud. The instruction to right click doesn't work on a standard mac install as by default right click is not enabled there. In that case, control click it and select: show package contents.