Patch Lookup Fields

[jsdanie1]

How do you properly patch a lookup field. for example, I just want to have a ribbon action that one click assigns a case for users.

Patch(
Accounts,
Self.Selected.Item,
{
'Account Name': Self.Selected.Item.'Account Name' & " Updated",
Owner: {
'@odata.type': "#Microsoft.Dynamics.CRM.systemuser",
systemuserid: "GUID_of_the_new_owner"
}
}
)

But this doesn't seem to do anything and the only example for patching is something stupid basic like updating the Account Name in the Microsoft Documentations.