How do I add an asterisk next to all fields in my form, so it is required?

You can easily set the field as required in the Form Builder. Here's how:

In the Form Builder, right click on your preferred field and then select the "Require" option.

You can also press "CTRL + A" in Windows to select all the fields in the form. After that, you will see a "Require" button at the top. Here's a screenshot:

Hope that helps. Thank you.