Explain a time when you didn’t know how to complete a task. How did you get the help you needed?

When due to some urgency and unfortunate incidents one of our team member was on leave and I had to prepare some invoice and dispatch the same on high priority basis. I was stuck in the middle due to some technical errors in the system when i had taken the help of one of my previous colleagues who helped me to get rid of the system error and I was able to generate the invoice and dispatch the materials successfully within the due time.