These instructions assume you installed Node-RED from an administrator enabled command prompt using the npm install -g node-red
command to do so.
As an administrator, install nssm from https://nssm.cc/download
And then from the directory where you installed nssm, run the commands
mkdir c:\temp
nssm install Node-RED "c:\Users\"%USERNAME%"\AppData\Roaming\npm\node-red.cmd"