Hi
nimal,
You cannot connect a POE switch directly to an NVR. A POE switch expands your routers network and needs to be connected directly to the network to do so. So just connect the POE switch directly to the router and then your NVR either directly to the router, or to the POE switch once it's connected to the router.
What do you have your cameras connected to? Both NVRs and POE switches have their own power supply, so will both will continue to power the cameras provided the cameras are connected to one of them.