How can I make non-required fields as required when other field is filled?

-in capture3.jpg all the requirements are aligned with me . but I have a small problem here .  The order is thickness , size , grade , qty   .  now I have marked all as compulsory but I want the other boxes compulsory  only if one fills in the thickness column .

You need to set the other fields as not required by default. Example:

Then, you need to add a conditional logic to require the fields when the thickness is filled:

 

https://www.jotform.com/help/367-How-to-Make-a-Field-Required-Based-on-Another-Field-Selection-or-Input

You need to do the same for the other fields. Here's my cloned version of your form showing the changes on the set of fields: https://wwww.jotform.com/61894157508970.