Can the Kong TCP type plug-in only work globally but not locally?

Question

I have a Kong TCP plugin, I use this for user validation. I find it can only work in global, but I want it to work only on some routers. When I add it to routers or services, it does not work. My steps are as follows 1 add the plugin with handler.lua and schema.lua 2 the handler.lua is like this

function MyAuthHandler:preread(conf)
    ...parsing header
end
return MyAuthHandler

3 I add plugin through web like konga, if I add the plugin as global, it works. But it does not work if I add the plugin to some routers

My question is： Is there any special setting required for locally effective plugins? Or is there some doc?