Moving Software Mirrored Drives To New PC

I have 2 drives that were using windows mirroring (Under Disk Management) in my old PC.

I've moved them to my new PC, but made a mistake.
I'm only running Windows 10 Home instead of Pro.
So when I imported foreign disks they came in as 2 separate disks instead of 1.

I've ordered Windows 10 Pro and plan on upgrading, but am unsure if I can re-import the disks so they appear as 1 since I already imported them.

Any suggestions?

Worse case I can probably reformat one of the drives, but I'm not sure if I can start a new mirror with a drive that already has data (and I really don't want to lose the data).

You could put them back in the old pc and break the mirror first (if the new pc already sees them as separate drives, then all you will have to do is to recreate the mirror when you upgrade your OS). This will give two disks with the same data on it. Then you can move one of them or both of them to the new pc and start a new mirror.

If it's a software RAID then there shouldn't be any issues simply moving the drives over, even if it were a hardware RAID, a mirror RAID is pretty forgiving and shouldn't break. You can break the mirror as suggested by play2mefish it won't harm anything since the drives are identical data.