Add certificates to a keychain using Keychain Access on Mac
A certificate file can be shared between computers. You can add certificates to your keychain for quick access to secure websites and other resources.
Go to the Keychain Access app
on your Mac.To open Keychain Access, search for it in Spotlight, then press Return.
Select either the login or System keychain.
Drag the certificate file onto the Keychain Access app.
If you’re asked to provide a name and password, type the name and password for an administrator user on this computer.