How can I add the sender to receive the form they are submitting?

By sender, you should be referring to the form owner. If that is the case, please set up a notification email on the form which will automatically send a copy of the form submission to the email recipient: https://www.jotform.com/help/25-setting-up-email-notifications

If you want to send a copy of the form submission to the person who is filling and submitting your form, you should setup an autoresponder email and map the email field on the form as the recipient email:

Please try and let us know if this helps.