Hello
Before getting your Access Token you have to register as a developer in Instagram and to receive Client ID.
Please visit https://www.instagram.com/developer and register a new app. You can get Instagram Access Token using Client ID. Copy your new Instagram Client ID then go to this page and paste your Client ID there.
The last step is, go to the Instagram addon settings (SP Page Builder Pro) and copy the Access Token to the input box provided. Then you are ready to display your Instagram Feed on your website
Have you followed these steps?