Editing a check template is currently unavailable in QuickBooks Online. If you want to add additional information on the paycheck like Account or Routing Numbers, add them in the Memo field to print it on the check.
You can also purchase pre-printed checks from us which includes this information. Click this link to open the Intuit Marketplace site: QuickBooks Checks & Supplies.
Having the option to customize a check format is a time-saving feature when added to the program. I know how beneficial it is to have this ability, so I'm personally relaying this feedback to our engineers for consideration. They are the ones who collates product requests and use them for future enhancements and program updates.
If you have any other questions about QuickBooks, feel free to post them here. I'll be glad to share additional insights and help. Have a lovely day!
Split-screen is currently unavailable in check. May I know on what page are you referring to? If you're referring to the category column and the amount column, you can adjust the width on it.
Also, if you're using the pre-printed check from a third party, you can check it in Apps Center or go to the Apps menu in QuickBooks. From there, you can search for check printing apps that integrate with QuickBooks Online.