Hello, and welcome!
You will need to log into your server on SSH and to tweak the NGINX configuration file up to the liking of LeanTime. This file is located in /etc/nginx/conf.d/business-suite.domain.tld/my_webapp.conf.
You can use the nano editor for example: nano /etc/nginx/conf.d/business-suite.domain.tld/my_webapp.conf Edit the file then save with CTRL+O and quit with CTRL+X.
If the app is simple enough, I guess it is only a matter of tweaking the alias statement to add public/ at its end, before the semicolon.
Then test that NGINX is happy with it with nginx -t, and if no error arises, reload it with systemctl reload nginx.