Way to pass arguments to FastAPI app via command line

I’m using python 3.8.0 for my FastAPI app.
It uses the .env file located on the root of a project directory. I am using the dotenv package, and the location of the .env file is hardcoded within the app. Here is my unit file

[Unit]
Description=Gunicorn instance for my_app
After=network.target

[Service]
User=nginx
Group=nginx
WorkingDirectory=/usr/share/nginx/html/my_app/
Environment="PATH=/usr/share/nginx/html/my_app/venv/bin"
ExecStart=/usr/share/nginx/html/my_app/venv/bin/gunicorn --bind unix:/usr/share/nginx/html/my_app/my_app.sock -w 4 -k uvicorn.workers.UvicornWorker app.main:app

[Install]
WantedBy=multi-user.target

The challenge is to run two versions (production and test) of the same app using two different .env on two different ports. I’ll have to create a second unit file. But how can I pass the name of two diffeent env file names to the app for further usage. These files contain database connections, etc.
I imagine it roughly like this
1st unit file

ExecStart=/usr/share/nginx/html/my_app/venv/bin/gunicorn 
--bind unix:/usr/share/nginx/html/my_app/my_app.sock -w 4 -k uvicorn.workers.UvicornWorker app.main:app --env_file_name=".env.prod"

2nd unit file

ExecStart=/usr/share/nginx/html/my_app/venv/bin/gunicorn 
--bind unix:/usr/share/nginx/html/my_app/my_app.sock -w 4 -k uvicorn.workers.UvicornWorker app.main:app --env_file_name=".env.dev"