Julie here from Shopify Support.
If your list is missing a store, that generally means that your store is associated with a different email address. You should be able to add your store to your Shopify ID by updating your email address in Settings > Plans and permissions > View account settings. We also have information on how to change your store owner account email that walks you through the process.
If you're still not seeing that particular store and your email address is the same one associated with your Shopify ID, then you'll just need to contact Shopify Support. Our Support team will be able to properly authenticate your account and help you connect your store with your Shopify ID.
I hope this helps! Let me know how that goes.