Hi!
First and foremost, backup everything you need. As far as I have understood you can boot to Windows 10 HDD? If so, back up everything you need from there and while you are there, please get me a fully expanded screenshot of Disk Management. After all of that has been done, we'll proceed. Sounds good?
Yes I can boot to Windows 10 HDD. I have backed up my what I wanted on an external drive. Here is the Disk Management: