How do I get a private key?

how do I get a private key?

Please note that when you enable encryption in your form, key file is downloaded. We do not save the key file on our server. If you have lost the key file, unfortunately it is not possible to recover it. 

I would suggest you to please disable encryption in your form to ensure that new submission you receive in your form are not encrypted. If you need to keep the encryption enabled, it is possible to generate new keys by disabling the encryption feature and then enabling it again. Use the CREATE ENCRYPTION KEYS FOR ME option to generate a new key. Please note that new key will not decrypt the submission data of old submission.

I would suggest you to please test your form again and get back to us if you have any questions:   https://www.jotform.com/help/344-Encrypted-Forms-and-How-to-Use-Them#What-Should-I-Do-If-I-Lost-the-Key-but-Wanted-to-Keep-Encryption-Enabled