To find #REF! invalid cell references within cell formula, you can use the "Error Checking" feature in Excel. Here are the steps:

1. Select the cell or range of cells that you want to check for errors.
2. Click on the "Formulas" tab in the ribbon.
3. Click on the "Error Checking" button in the "Formula Auditing" section.
4. Excel will display a dialog box with a list of errors found in the selected cells. Look for the error "Invalid cell reference error (#REF!)".
5. Click on the error to see the details of the error, including the cell reference that is causing the error.
6. Click on "Trace Error" to see the cells that are dependent on the cell with the error.
7. Correct the error by updating the cell reference or deleting the formula if it is no longer needed.

By using the "Error Checking" feature, you can quickly identify and correct any #REF! errors in your formulas, ensuring that your spreadsheet is accurate and reliable.