Configure a Certificate setting in Apple Business Essentials
Certificates are a crucial part of device security. They’re used to check the validity of an organization’s website, access networks, sign and encrypt mail messages, and more. Certificates are also used when FileVault is turned on for a Mac in your organization.
iPhone, iPad, and Mac computers come preinstalled with certain Root certificates. Root certificates are used on the internet to verify websites (using https) and your organization may also have their own root certificate or other certificates they want all users to have. Most certificates are signed and contain a public key, information about the website, network, or user, and are signed (verified) by a Certificate Authority (CA). Apple Business Essentials supports certificates in the Privacy Enhanced Mail (.pem) format.
Important: Certificates generally expire after 1 year, so if you are sending certificates to devices, you should set a reminder for 11 months after the certificates were created to remind you to either renew or replace the certificates.
See Intro to certificate management for Apple devices in Apple Platform Deployment.
In Apple Business Essentials, sign in with a user that has the role of Administrator.
Select Settings
in the sidebar, then select All Settings.Select the Add button
next to Certificate 
.Under Platform, select the operating systems you would like to configure this setting for.
Enter a name for the certificate, select Choose file, select your certificate, then select Upload.
Select Save.