In the Certificates section, click the plus sign (+) to add the certificate.
In the Production section, select In-House and Ad Hoc.
Generate a certificate signing request (CSR) by using the Certificate Assistant.
Follow the instructions that Apple provides on the CSR screen.
Upload the CSR to the iOS Provisioning Portal, and download the distribution certificate.
Save the certificate, and open it with the Key Chain Access application.
Use this certificate to sign iOS applications.
To export this certificate to a different build, save it in .p12 format:
In Key Chain Access, go to the My Certificates section.
Right-click the downloaded certificate, and click Export.
Save the certificate in .p12 format, and provide a secure password when required.