Telling the user what to do in specific step of the form

I have a form in steps, The user should fill the required data in each step to be able to go to the next step and this is working fine.

But there is a step that some users don't know what to do in this step, There are 3 checkboxes the user should at least check one of them, Then enter the related data to go to the next step.

The user could choose all the 3 checkboxes, But he has to enter all the 3 related data, So whenever a checkbox is checked the related data should be filed to go to the next step.

So what text/hints/images/styling should I use to let the user know what to do?