Add the following in Advanced tab
location / { return 301 /admin;}location /admin { proxy_pass [url=http://<Pi-hole-IP>:<Pi-hole-Port>/admin;]http://<Pi-hole-IP>:<Pi-hole-Port>/admin;[/url] proxy_set_header Host $host; proxy_set_header X-Real-IP $remote_addr; proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for; proxy_set_header X-Forwarded-Proto $scheme;}
replace the IP and port