unfollowUser.js

const { IgApiClient } = require('instagram-private-api');

const ig = new IgApiClient();

ig.state.generateDevice(process.env.USERNAME);

(async () => {
    await ig.simulate.preLoginFlow();
    /*
        Authenticating
     */
    const auth = await ig.account.login(process.env.USERNAME, process.env.PASSWORD);
    const followersFeed = ig.feed.accountFollowers(auth.pk);
    const followingFeed = ig.feed.accountFollowing(auth.pk);
    /*
        Getting followers
     */
    const followers = await getAllItemsFromFeed(followersFeed);
    /*
       Getting following
    */
    const following = await getAllItemsFromFeed(followingFeed);
    /*
        Making a new map of users username
     */
    const users = new Set(followers.map(({ username }) => username));
    /*
        Filtering through the ones who aren't following you
     */
    const notFollowingYou = following.filter(({ username }) => !users.has(username))

    /*
        Looping through and unfollowing each user;
     */
    for (const user of notFollowingYou) {
        /*
            adding a 1000, so it can always be above 1 seconds delay.
         */
        const time = Math.round(Math.random() * (6000)) + 1000;
        setTimeout(async () => {
            await ig.friendship.destroy(user.pk);
            console.log(`unfollowed ${user.username}`)
        }, time)
    }
})();

/*
    Source: https://github.com/dilame/instagram-private-api/issues/969#issuecomment-551436680
 */
const getAllItemsFromFeed = async (feed) => {
    let items = [];
    do {
        items = items.concat(await feed.items());
    } while(feed.isMoreAvailable());
    return items;
}