I don't believe I ever received a private key. Where would I find it? Was it sent via email?

@Jeff_Crompton

Have you decrypted submissions before?

The private key, when downloaded, is saved to your device's download folder so you can check the private key whether is there or not. The private key file extension is .key so you can use that to search your private key on your system/device.

However, if you forget to download the private key for your encrypted form before then there is no way to decrypt the current submissions on your form.

It is possible to generate new keys. However, the new private key will not decrypt the old data. To generate a new key, please follow this guide: Encrypted-Forms-and-How-to-Use-Them#How-Can-I-Enable-Form-Encryption

Please be sure to download the new private key and save it somewhere safe. You can also send it to your email in case your OS system is broken, you can download the private key from your email.