Change nginx default folder - reactjs

Question

Here what I have done:
1/ Use Google cloud as a server (Ubuntu 18) for admin page.
2/ Have a project react-js app, ex: abc
3/ Encrypt website www.sub.abc.com successfully, point to IP (Godday domain) on Google cloud successfully. (Source: https://linuxhint.com/redirecting_http_https/).
Problem: My app can not run on port 80, nginx took it! I have search many instructions but they
are not clear.
What I have done to fix this:
1/ Edit config file of nginx (https://www.tecmint.com/change-nginx-port-in-linux/).
2/ Export port 80 in my app. (export port=80 npm start).
Can not run my app on port 80 because something has taken that port?!
If I kill port 80 ===> nginx turn off.
Please give me the right way to change config file or replace nginx default folder to my app folder. Thank you!
I have deployed successfully. If you have the same problem. Can follow this.
DEPLOY
NPM + NODEJS
$ sudo apt-get install curl
$ curl -sL https://deb.nodesource.com/setup_13.x | sudo -E bash -
$ sudo apt-get install nodejs
NGINX
$ sudo apt update
$ sudo apt upgrade
$ sudo apt install nginx
CONFIG
cd /
sudo mkdir app
sudo mkdir api
sudo mkdir html <=== git clone ...
cd /etc/nginx/conf.d
sudo touch api.conf
sudo vi api.conf

Answer 1

you can use the nginx as reverse proxy and change the port of you app for another like 8000 for example and configue in nginx:
server {
listen 80;
location / {
proxy_pass http://127.0.0.1:8000;
}
}
I have deployed successfully.
If you have the same problem. Can follow this.
DEPLOY
`$ sudo apt-get install curl
$ curl -sL https://deb.nodesource.com/setup_13.x | sudo -E bash -
$ sudo apt-get install nodejs`
NGINX
`$ sudo apt update
$ sudo apt upgrade
$ sudo apt install nginx`
CONFIG
`cd /
sudo mkdir app
sudo mkdir api
sudo mkdir html <=== git clone ...
cd /etc/nginx/conf.d
sudo touch api.conf
sudo vi api.conf`