Hey DaveGY,
But as far as i understood this ESXi you mention is the existing one that holds the productive VMs. What i am saying is this:
- Re-install the ESXi 7 with version 6.5
- Add it to vCenter Server.
- Execute the migration of vCenter Server to version 7 pointing to this ESXi
- Update the new ESXi to version 7 using vSphere Lifecycle Manager.
- Migrate the VMs from the old ESXi to the new ESXi.
- Decommission the old ESXi 6.5
Take into account that this new ESXi even if it is standalone you will need to put it in a cluster (unless you do not have one configured) with the EVC in the CPU level of the older ESXi so you can vMotion the VMs without powering them off.