Problem upgrading from 2 bay to 4 bays

Had bay 1 & 2 with 4TB discs each in RAID 1 (Vol 1) which became full eg over 95%. I have since deleted 1.3TB
Added a 4TB to each of bay 3 & 4
Seems made the mistake of asking Vol 1 to expand expecting it to add the 2 new disc.
Now stuck with red LED on disc 1 with the display telling me to replace it and the Dashboard telling me it is expanding and to replace disc 1 and that Vol 1 is degraded. All disks are shown as good.
Tried robooting and putting one of the new discs in bay 1 but still get the same display.
Tried changing to RAID 5 which I think would be correct but that wants to reformatt all discs and there is no option to migrate.
Could anybody offer any advice?

Hello ColJenWD,

You can refer the link provided below for more information on RAID migration.