What is the best way to migrate Azure Functions from one tenant to another?

The best way to move/migrate your Azure Function from one tenant to another is by changing publishing profile in your Azure Function’s Visual studio deployment solution.
Simply download new publishing profile from new tenant and use that profile to deploy your Azure function.

Alternatively, question should be How to move/migrate Azure function to one Azure subscription to another?
Also, you can perform this action from Azure portal, simply select your Azure Function from resource group and click on MOVE button from top navigation properties, then select move to another subscription. Then provide subscription details and its done.