hox to enhance the length of a label ( example is following)

nom et prenom du beneficiaire is too short !

Thanks

You can inject this to adjust the width of "nom et prenom du beneficiaire".

input#input_51 {

    max-width: 900px!important;

    width: 694px!important;

}

To adjust the width to your desired preference, simply change the value of the yellow highlighted code.
Here's a guide on how top inject css: How To Inject Custom CSS Codes

Here's a link to the cloned form where I tested the CSS: https://form.jotform.com/60657793326970 
You can clone it to your account by following this guide: How To Clone A Form

If you need further assistance, do let us know.