You can enter your Shopify username to sign in with Shopify.
Example: If your Shopify Admin URL is beauty.myshopify.com/admin, then your shop user name is beauty
If you have previously installed the app, and created a password, you can login with your credentials here.
We can help you recover your login credentials. However, it is also possible that you have never created a password.
If you do not remember creating a password, you can login through your Shopify store's APPS section.