Upgrade MyCloud Mirror HDs

Hi. PLEASE can somebody help me!
I have a MyCloud Mirror 2, Both 2tb drives failed after installing OS5. (" days apart).
OK I thought, I would use the opportunity to upgrade the drives to 2X3, and bought the corrrect WD Red drives. I replaced them…easy!
The data was saved, all good except for two problems, the capacity stayed at 2x2tb, even though the admin showed I had 2x3tb. Also, I had one blue light out on the front. (pictures attached)
Can anyone give me a step by step instruction on how to fix this? I’ve tried with WD and their help is hopeless, I’m not an IT engineer, just a simple home user who is a bit thick!
I would be so… grateful if someone l help.

Many thanks, Alan