Check the new configuration:

$  docker container exec <<< container name >> nginx -t
nginx: the configuration file /etc/nginx/nginx.conf syntax is ok
nginx: configuration file /etc/nginx/nginx.conf test is successful
$

Apply the new configuration:

$  docker container exec <<< container name >> nginx -s reload
2019/05/20 19:14:29 [notice] 7#7: signal process started
$