Remove local storage in guest VM

Dear all,

I would like to ask how to remove local storage under the summary tab > Storage section as this Guest VM already moved to the SAN storage. (attached local.jpeg)

However, when I right click unmount the local storage, it gives an error message saying "For successful datastore unmount the following requirement must be fulfilled" --> No virtual machine resides on the datastore  <-- with a red cross sign. (attached error.jpeg)

This local datastore did have the vm inside but however I just want it not to appear in the guest vm.

Appreciate or your help.

thank you