The general process for getting an early release of Veeam Backup & Replication 9.5 Update 1, which adds support for vCenter 6.5, is making a support ticket with Veeam asking for the RC.

If you don’t want to go through that hassle you can just download it directly here: https://download2.veeam.com/veeam_backup_9.5.0.802.update1.RC.zip

Usual disclaimer applies: is not official release software etc. etc. etc.