Insomnia REST Client - Cannot set Content Type in multipart Form

Question

When making an API request for "form-data", I need to set content-type application/json for the "mailInfo" field (shown in the screenshot below) in Insomnia. I can toggle this option in Postman but I don't seem to find a similar option in Insomnia.

I am using Insomnia 8.4.2

Please help!