I can help you import your customized templates, NOAT.
After you've turned on the option to import style, did you refresh the page or tried loggin out and logging back in? We'll need to refresh the page to update changes. You can do so if you haven't yet.
A browser-related issue might have the changes not to update. You'll want to log in to your QuickBooks Online account using a private browser and then follow these steps to turn on and use the Import Style option.
Click the Gear icon at the upper-right, and click QuickBooks Labs.
Turn off and then turn on Import Style.
From the Gear icon, click Custom form styles.
At the upper-right, click the New style drop-down to see and select Import style.
If you're able to do see these options, you can switch back to the main browser and clear the cache. Other supported browsers can also help you isolate these kinds of issues.