Ciao
If I understand correctly you need to upgrade a vSAN infrastructure from 6.5 to 6.7, and the current vCenter that manages the vSAN infrastructure is not hosted on the vSAN datastore itself.
I would say that you can take point from this guide, considering that the new update of vCenter from 6.5 to 6.7 is an installation of vCenter 6.7 with a copy of the data from 6.5.
vSphere 6.7 upgrade vCSA 6.5 to 6.7 - pt.2 • Nolabnoparty
Also in the same guide there are also the steps to update ESXi hosts and vSAN
However, always check the HW compatibility matrices, interoperability between ESXi versions and upgrade path