Log in to your Apple Developer account with your main Apple ID, not the new one that you just created, and follow the steps below.
1. Click on Identifiers.
2. Click the your App from the list.
3. Scroll down to Push notification & press configure
4. Click on the create certificate button for Development SSL certificate.
5. Download the CSR file provided here to your desktop (CSR file)
Choose the downloaded file, and press continue.
6. Download the certificate & store it safely, you need to share it with MyStudio dev team.