This is Elias from Shopify Support. I'd be happy to lend a hand with this!
I understand you've uninstalled the app, Low Stock - Back in Stock Pro, and tried editing the code already, but the app's message is still appearing on your store. One option you can try is to roll back to an older version of your theme, which will allow you to choose an earlier version for a particular theme file and revert the changes. While you do need to know which file was modified by the app previously; however, this method is very simple to use and shouldn't require you to modify any of the coding.
If rolling back to an older of version of your theme file isn't working, then I've also found the developer's step-by-step help you with this - How to uninstall Low Stock - Back in Stock : Ordersify. It's worth mentioning that the developer is always available to assist you as well - if you need to reach out to them, you can do so through the contact information found in the Support section of their app's page.
If neither of these options helps you resolve the issue, then our Support team would also be happy to assist you. Though I'm unable to take a closer look at your account, as we're unable to provide account-specific support via the Community Forums. However, our Support team can help you through live chat, email, or callback. To begin a support request, please visit the Shopify Help Center and log in to your account.
I hope this helps you with uninstalling the app's coding from your theme. Feel free to keep me posted!