Kentico 13 Fields tab not visible on Forms

I'm using Kentico 13 .NET Core development setup. However, I dodn't see the 'Fields' sections for Forms in the left menue like I used to do in older versions. I want to add some custom fields to the database table of the form and aslo want to change the data type to int on some of the fields. How can I do this?

The forms tab is no longer available in v13. You use the form builder to add your custom fields and set the visibility to false. If you want to have different types of form controls, you can create your own.