You've come to the right place, @bsingle-uab-edu. I'm here to help you create custom fields for import in QuickBooks.
You can still import the file if it's still existing in QuickBooks. If you haven't created custom fields, you can follow the steps outlined in this link.
Then, you can now prepare your file to be imported into QuickBooks Online. To start, set up the necessary fields in your QuickBooks Online account.
Please note the file with transactions you want to import, has to include new columns with the name of your new custom fields. Also, make sure you have mapped the labels with the name of your Custom fields in the Mapping step.
Go to the Gear icon, then Custom Form Styles.
Select the New style drop down menu, then Import style.
Choose a form type.
Choose Upload your .DOCX file field, then find and select your .docx template.