@sim80n This should just be a case of changing the IP on the vsan-tagged vmk interface of the Witness. Validate the clusters data is healthy before doing so via Skyline Health.
You should of course validate that the data-nodes can reach this and not need things such as static-routes etc. .
An alternative would be to just deploy a new Witness with the new IP and replace the current one with it via the 'Replace Witness' button in the vSAN Fault Domains UI.
