Save values to a .env variable in ReactJS

I've been trying to create a .env variable where initially it will be empty but after login process it will store the data to the .env variable for further work, but unfortunately, I am not able to do so.

Before I put my code example, I would like to have some suggestions!!

Yea, in the login process I'm using session storage to store the user token. So, will it be a good work to store the user data into a .env file and later access it for future use or should I just call getToken function every time I need the token to verify if the user is logged in.

login.js:

    const getToken = () => {
        const tokenString = sessionStorage.getItem('token');
        const userToken = JSON.parse(tokenString);
        return userToken?.token
    }

    const saveToken = (userData) => {
        sessionStorage.setItem('token', JSON.stringify(userData));
        setToken(userData)
    }

Tried different techniques to make it work, but I just couldn't get the data from the .env file. Watched many different YouTube videos and did exactly like them but it was all in vain. I checked multiple timed if there is any type or bug in my code or not! There was no error. I was getting the token after successful login and by default it was returning null. I was storing the token only when the user login successfully so that no garbage value gets inserted into the value.

Here's my logic:

const handleSubmit = async function (e) {
    e.preventDefault();
    const response = await loginUser(user);
    if (response.status === 200) {
        setToken(response.data);
        process.env.REACT_APP_USER_TOKEN=response.data;
        navigate("/");
    } else {
        console.error(response)
    }
}