Windows 10 Pro 2-disk mirrors 'access denied'

I have been running 2 Freenas 2-disk mirror PC’s for a number of years (final version 11.3-U5). The 1st Freenas PC backed up a Windows 7 Pro x64 PC & the 2nd Freenas PC backed up the 1st Freenas PC using Allway Sync 21.0.9 Pro.

I upgraded the Windows PC to Windows 10 Pro x64 & discovered that I’d lost access to the Freenas PC’s (something about Win 10 doesn’t allow ‘guest’ account access).

The only way I could regain access to each mirror was to create a dataset for each 2-disk mirror to allow me to edit permissions, choosing a new user & group. Now I could backup my Windows 10 PC but ONLY to the datasets I just created. The backups created when my PC was Windows 7 were visible but no longer accessible. I wanted to delete these old backups as they were of no use to me but I’m prevented from doing so due to the access issue.

Is there any way I can gain acces to these old backups? I’m not familiar with the intracies of Freenas so keep any advice simple

ps

I’ve just upgrade my Freenas 11.3-U5 to Truenas 12.0 U6