At first, if you have specific VxRail questions, contact Dell EMC Hyper-Converged Support. Because only general VMware questions are answered here and HCI systems can be special in some ways. Second, it's always good to tell the people here what versions you're using, as there may be differences in how to do something depending on the version.
To give you a general answer:
The vCenter of VxRails is not really different from a normal vCenter. So you can make normal file based backups using the VAMI backend: