Adding new hard drive

I know the title sounds like every single other topic that seems remarkably similar, but I am in a pickle.

I initially put a 3TB hard drive in here and formatted it as JBOD because I am putting easily replaceable data on it. Then I ran out of space.

I hurriedly added another 4TB hard drive, and came to a pickle. How do I format this? It is now Volume 2 because I formatted it as JBOD again. I was hoping to format both of them as JBOD, but is there anyway to keep the data while I do that? Or am I stuck as 2 separate volumes?

usually each disk in windows has a drive number and a drive letter