I'm a guy who manages people who manage people. It's really important that you let the person who gave you the task know that you don't know how to do it. They may be able to help, or they may have a better use for your talents. Not telling them means you need to spend the time to acquire the skills to do the job, which may be a one-off, while they wait with increasing frustration and a lack of understanding of what the holdup is.

The person who gave you the task is at fault for not confirming that this is within your skillset. So don't feel like this is all on you.