So you say that this instructions do not work for you?
What is the issue? Can you post screenshots?
Yours is the second case now (that I’m aware of) where a Synology user reports a “failure to access” issue with a migrated (from old NAS to new NAS) storage pool (Error Loading Folder: Unauthorized on Synology DS1520+ in Roon Setup (ref#VUWXC1)). Maybe something gets messed up during this migration, Synology support is probably the better option to get help on this or at least a worthwhile additional source for troubleshooting.