Multiple App with .env

Hello everyone
I am looking to use .env environment files with an instance composed of several applications.
For example, I want to have several applications on the same CodeIgniter instance but with different configurations (Example: baseUrl, database, etc.)
How would you proceed?

My structure on CI v4.5.0:

app1
     Config
     Controllers
     Database
     ..
app2
     Config
     Controllers
     Database
     ..
app3
     Config
     Controllers
     Database
     ..

Thanking you in advance.
Pierre