Implement a Leas Assignment Rule inside a Workflow Rule

I am a user of several Zoho modules. Currently, we are using Zoho Forms to take inquiries on our website, and sync with the CRM with Trigger Workflows. The workflows send some emails and it works fine. But then I need to add to that workflow rule that the Lead Owner be assigned via a round robin Lead Assignment Rule. Zoho allows this to be done very easily with the default CRM webforms, but not Zoho Forms.

What appears to be the specific need is that the "Edit Workflow Field Updates" dialog needs to have an option for an Assignment Rule. It does not. Is there a way to do this? My impression is that there is not at this point.

I see that a workflow can have an Update that is "Assign using active assignment rule" but at see no place to specify which that is. That would be helpful.

We can also assign a Custom Function --> Round Robin Plugin, but this simply does not work. Zoho ignores it but processes other workflow commands.