The same thing happened to me and I can help you first you need to request the change of keystore, you send the .pem file when they tell you that it was changed use your new keystore and with apk-signer in the play store you can sign your apk with your keystore with format .p12
P.D: You need...
They should add functions such as automatic updates without the need to create apk
For example:
To add videos without needing to update the apk
In-app rating
Comments system and profile
Another necessary request would be that it could already release versions for iOs