We have exchange 2013 in a hybrid evironment with Office 365, now we need to install C8 to our on-premise Exchange 2013. Is there any document around to walk me through ? Because when I ran "Setup.EXE /IAcceptExchangeServerLicenseTerms /PrepareAD" I just got kicked out and somewhere in the log it says "A hybrid deployment with Office 365 has been detected.  Please ensure that you are running setup with the /TenantOrganizationConfig switch"

Hi,

According to your description, I understand that failed to upgrade Exchange 2013 to latest version with hybrid environment, and return error A hybrid deployment with Office 365 has been detected.  Please ensure that you are running setup with the /TenantOrganizationConfig switch.
If I misunderstand your concern, please do not hesitate to let me know.

I find an similar thread about your question, for your reference:
https://social.technet.microsoft.com/Forums/exchange/en-US/f1827b3e-f683-4935-b5e5-e554bc513e1a/exchange-2013cu1-install-with-existing-office365-hybrid-configuration?forum=exchangesvrdeploy

Summary:
1. Run PowerShell as administrator, then entry below command to connect to Office 365:

$Session = New-PSSession -ConfigurationName Microsoft.Exchange -ConnectionUri https://ps.outlook.com/powershell/ -Credential (Get-Credential) -Authentication Basic AllowRedirection
Import-PSSession $Session

2. Provide the account name and password, for example administrator.

3. Once connection completed, run below command to obtain the XML configuration file:
Get-OrganizationConfig | Export-Clixml -Path C:\Test\MyTenantOrganizationConfig.XML
4. Re-run Setup as below:
Setup /PrepareAD /IAcceptExchangeServerLicenseTerms /TenantOrganizationConfig:C:\Test\MyTenantOrganizationConfig

Thanks