I'd recommend just formatting it as a new partition.
I tried recently to overcome the same issue for the same reason using different tools such as gparted without success. After trying hard enough I succeeded in mangling up the drive to the point that I had to reinstall Windows.
I've been told that Paragon Hard Disk Manager can actually move those unmovable partitions without problems, at least the MacOS version, but haven't tested it myself. The product description does mention split/merge and redistributing free space, which sounds promising.
It's also available for Windows. It's a paid product. There might be a free tryout, but should you try it I'd recommend doing a full system backup first; or at least backing up your data.