Ask the client to provide you with Certificate.p12, which will include the certificate and private key.
To create .p12 goto keychain access, select the certificate option in the second block in the left pane, and then select the certificate you want and right-click> Export> Enter the password for p12> enter mac passowrd> save in the right place.
To install on your side, just open the client click p12 to open it and enter the password that the client entered for p12.
Finally, you have finished receiving the distribution certificate, which is signed at the customer site.
Please vote for me and mark as the answer, if he fulfills your requirements.
Thanks,
Ronak source share