I lost my .keystore file?
Faced the same problem. I was trying to restore it via deleted files restoring tools, but it failed. So, there is no other way: you should issue another application.
Generally, the only advise that exists on keystores: "always back it up!"
Now it is possible don't worry, here is the full and final steps to reset .JKS file.
UPDATE: As it states in the Play Console Help here (scroll to bottom), you should now already do step 3 before (create new .jks, convert to .pem) and only then fill out the form with the upload_cert and .pem file attached. This will make the support process easier and faster for you.
Step-1
Download the UPLOAD CERTIFICATE (file name - upload_cert.der) from your Google Play Store Console
Step-2
Go to this LINK https://support.google.com/googleplay/android-developer/contact/key?hl=en And fill the application form with your valid Email ID and upload the file (upload_cert.der).
Step-3
Now you will get the Email from support team, and they don't need your .JKS file but .PEM file here is the email Sample.
Step-4
to convert .JKS file to .PEM file you just have to download KeyStore Explorer
After replying the Mail, wait for 48 to 72 hours your keystore fill will reset.
Until today, losing your key would make it impossible to update your app with a new version. In such cases, the only solution was to publish a new app, with a new package name and key, and ask all of your users to install it.
Starting from today, the app signing key in the Play Console is now securely managed by Google Play meaning that you are only responsible for managing your upload key. If your upload key is compromised or lost, Google's developer operations team can assist by verifying your identity and resetting your upload key. Google will still re-sign with the same app signing key, allowing the app to update as usual.
For existing apps, it requires transferring your app signing key to Google Play. For new apps, Google can generate your app signing key. Once enrolled in app signing, you sign your APK with an upload key, which Google uses to authenticate your identity. They'll then strip that signature and re-sign your app with the app signing key.