We have outlined the steps for you so you can try resetting your password
Go here to edit your Instagram profile (login with Facebook if you have to):https://www.instagram.com/accounts/edit/
Enter an email address & and a username if those fields are empty
Log out of Instagram
Go here to reset your password and enter your email: https://www.instagram.com/accounts/password/reset/
Open your email and press the link in the email you should have received from Instagram.
Set a new password
Open Plann and use the IG handle & the new password to login