To access your data from Instagram, go to Profile > Settings > Privacy and Security > Data Download--Request Download and select "JSON" from the options.
Instagram will email you a look when your data is ready, simply follow the link to download.
You will want to JSON files from the "followers_and_following" subfolder: followers.json and following.json.
Use git clone https://github.com/winiboya/follow-back.git to download the code or copy and paste the code in followback.py.
Save your followers.json and following.json files in the same folder as followback.py.
Run the code using python followback.py in the appropriate folder.