How to enable custom plugin from kong manager?

We are running kong (kong/kong-gateway:3.0.0.0-alpine) with kong-manager (free mode) as docker container. We have coded a custom plugin that we do install in the running kong container through the below commands. I do not see this plugin on kong manager UI. How can I see my custom plugin and enable it for a service or route?

docker exec -it --user root $container mkdir /usr/local/share/lua/5.1/kong/plugins/$dir

docker cp plugin/. $container:/usr/local/share/lua/5.1/kong/plugins/$dir

docker exec --user kong -e KONG_PLUGINS="bundled,$dir" $container kong reload -vv

Thanks.