Our Spanish Support agents are busy helping other Jotform users right now, so I'll try to help you in English using Google Translate, but you can reply in whichever language you feel comfortable using. Or, if you'd rather have support in Spanish, let us know and we can have them do that. But, it might take a while until they're available again.
Now, coming back to your question, If you want to limit the submission with the same value inserted in a field, you can do it from the form settings. Here's how to do it:
In Form Builder, click on Settings.
Select Show More Options.
Scroll down to Unique Field and select the field from the dropdown.