Firt of all you have to update the “nginx.conf.sample”,
You can find this file at magento root, so change
location ~ ^/(index|get|static|errors/report|errors/404|errors/503|health_check).php$
TO
location ~ ^/(index|get|static|errors/report|errors/404|errors/503|health_check|mycustomfile).php$
Here I want to run mycustomfile.php so I will place this file in “pub” directory.
After this you have to reload the nginx by runing this command on ssh
sudo nginx -s reload
Hope it will help you