Hi Stephen,
Please follow below steps,
1. Go to Reports tab
2. Click on "Custom Reports"
3. Click on 'Create Custom Report'
4. Enter a name, description and select the domain
5. Choose desired Report type
6. Under Report category, Click on 'Logon Activity' and select ' Logon Failures '
7. Under Charts, Select Graph type and choose a field that would be primary X axis
8. Under Filters, Click on ' Add Filter '
9. Add the following correlation,
User Name -- Equals -- <Click on the value field and select specific OU>
10. Save the Report
Hope it helps.
Regards,
ADAudit Plus Team