Hi Jamie
I am Dave, an Independent Advisor, I will help you with this . . .
Open Disk Management (accessible by right clicking your Start Button)
In the bottom pane of Disk Management, right click any partition on that SD card and choose 'Delete Volume'
Then, when the whole drive is marked as 'Unallocated Space' right click that and choose New - Simple Volume, accept the defaults and apply that
If that does not resolve this, then please provide a screenshot of that Disk Management window