- First, save you mount information:
mount -m > saved_mount_info.txt

- it will show something similar to the following:
06:10:17> mount -m
mount -f -s -b “C:/Cygwin/bin” “/usr/bin”
mount -f -s -b “C:/Cygwin/lib” “/usr/lib”
mount -f -s -b “C:/Cygwin” “/”
mount -s -b –change-cygdrive-prefix “/cygdrive”

- print this or have it showing in another window.

- now unmount everything:
umount -A

- now for each line in your saved printout, use the mount command to mount to your *new* drive location, e.g.:
mount -f -s -b “D:/Cygwin/bin” “/usr/bin”

..etc for each line in your printout