QB Issue Resolution:
You can’t with QBO plus version.
However, with the QBO Accountant version, it comes with Accountant toolbox. With that, it’s possible to add Class Tracking on historical transactions for invoices (item-based) and expenses (account-based).
You will need to check with your Accountant for help.
Resolution for Issue 'Using QBO Plus, if you turn on class tracking, is it possible to add classes to historical invoices from previous years or expenses from previous years?' available: Yes (Solved).
Source: Intuit Community forum.
Using QBO Plus, if you turn on class tracking, is it possible to add classes to historical invoices from previous years or expenses from previous years?: this issue or error code is a known issue in Quickbooks Online (QBO) and/or Quickbooks. Support for this issue is available either by self-service or paid support options. Experts are available to resolve your Quickbooks issue to ensure minimal downtime and continue running your business. First try to resolve the issue yourself by looking for a resolution described below. If it is a complex issue or you are unable to solve the issue, you may contact us by clicking here or by using other support options.Support for class tracking
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Error Recovery for class tracking [Canada]
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