Open Xcode, go to Settings → Accounts Tab.
Add an account with your Apple ID.
Click “Manage Certificates…” and add a new certificate.
Open Keychain Access, select the login keychain.
Click on the “My Certificates” tab. There should be an “Apple Development” entry with your Apple ID.
Double click on that entry, in the details copy the string next to “Organizational Unit”. That’s your team ID.
