Thanks for trusting your concern to us. I can provide information with regards to recovering a deleted template.
At this time, there's not a way to retrieve a deleted template in QuickBooks Online.
While the feature you need isn't available, I encourage you to send feedback straight to our product developer to let them know you'd like this added. QuickBooks Online is a constantly evolving platform and the voice of users, like yourself, helps steer the changes that occur.
Go to the Gear icon.
Enter your request/product suggestion, then click Next.
Select Feedback as the Category.
Click Send message.
Additionally, I want you to know that your voice matters and I'm going to submit feedback based on this interaction. Feedback is sent to the Development Team for determining what features and systems to implement for users.
For future references, I'd like to leave some helpful articles and tutorial about the Custom Form Styles in QuickBooks Online: