Rancher NFS Change From V4 to V3

We need to change Rancher NFS to use nfsvers=3 instead of nfsvers=4. I see the MOUNT_OPTS in the nfs-driver container under Command / Environment, but I cannot find a way to edit the values.
We are running Rancher 1.6.2 and rancher/storage-nfs:v0.8.3
I am new to Rancher, so any help will be appreciated.