Certificate based Site-Site-VPN with two ASGs

Sorry, here I’m again.
I’ve got no problem establishing a PSK-based site-to-site-IPSec-connection between to ASGs (one with a fixed IP, the other can be resolved via dynDNS).
But I failed to create a certificate-secured IPSec-site-to-site-connection.
I don’t find the possibility to move the public-cert from one to the other ASG.
Do I think completely wrong?
Can anyone provide a link to a step-by-step-guide?
Thanks in advance… J.Kontny