how to patch and download the patch

用您的Veeam账号登录，选产品，在对应产品下选“download patch” 。 有些特殊补丁需要根据KB下载或support提供

As I understand you need to patch Veeam v 9.5 which as I know is out of support, you need to upgrade to v12. Reference to v12 release notes you need to contact Veeam Support:

Veeam Backup & Replication 12 supports automated in-place upgrade from any version 11 build and from version 10a (build 10.0.1.4854), which preserves all product settings and configuration. To upgrade from earlier versions, please contact our Customer Support.