Julie here from Shopify Support.
You can close any of your existing Shopify stores by heading to Settings > Plans and permissions > Close store. We also have a help doc on how to close your Shopify store that will walk you through the process.
Keep in mind that you must be able to login in order to close your store. If you are unable to login because your store is frozen, then there's no need to close your store since it's already inaccessible and wouldn't be receiving any charges.
If you have multiple stores and you aren't quite sure which ones are still active, then you can always use the store recovery tool. There, you can enter the email address you would have used when you first signed up and you'll receive a list of stores associated with that particular email address.
I hope this helps, but if you still need assistance with any of your stores, feel free to contact Shopify Support directly. They'll be able to authenticate your accounts and make sure that you've closed any stores you no longer wish to use.
I'd also love to help you with your print on demand apps. To get started with Printify, you'll just need to install their app from the Shopify App Store here. Once that's done, you'll be able to start browsing their products and importing them into your own online store. Printify actually has some excellent resources on how to get started using their app over in the Printify Help Center, which you can access right here. We also have a great course, "Build a Print on Demand Empire" that will walk you through the process of creating a successful print on demand store, step-by-step.
If you need any help using Printify, then you'll just need to contact the developers directly; when it comes to third-party apps, the developers themselves are the best to assist. You can generally reach out directly through the app itself, under a Support or Help section. The developers also have live chat available on their website.
Pillow Profits, on the other hand, isn't available in the Shopify App Store. Is there a reason why you're wanting to use this particular app? Generally, most merchants will stick to one print on demand app, so I'd love to help you find one that suits your business' needs the most.
What kind of products are you wanting to sell? Is there a particular product that Pillow Profits offers that isn't available through Printify?
Looking forward to your response!