Angular how to change environment variable values after build

Sample environment variables for development & production environment.ts

export const environment = {
    env: 'Dev'
};

environment.prod.ts

export const environment = {
    env: 'Prod'
};

In the above code using the window object like below:
environment.ts

export const environment = {
    env: window['env'] || 'Dev'
};

environment.prod.ts

export const environment = {
    env: window['env'] || 'Prod'
};

Create a .js file in the root directory and add it to index.html file as a script

<script src="./config.js"></script>

In the config.js file, you can update the environment values without rebuilding your application like below:

window['env'] = 'Uat';