RAID mark disk as good

A disk on a RAID5 configuration failed
When trying to replace the disk, the technician by accident disconnected another of the good disks, therefore causing the RAID5 to be marked as failed.

Is there a powershell command to mark the pseudo-failed disk back as good and set the RAID5 status back to degraded ?

Not with native cmdlets.

It’s possible the manufacturer of your RAID controller provides a cmdlet that allows you to manage the status but without further details about your server no one will be able to advise you.

My experience with HP is that putting the accidently removed disk back in and replacing the failed disk will usually let you recover the array through the Array Configuration Utility. I’d look at that or the equivalent software for your controller