how to reset my macbook to default setting?

What to do before you sell, give away, or trade in your Mac - Apple Support

wong2568 wrote:

I want to clear up all my personal data before selling it out

The link posted above is a hotlink:

What to do before you sell, give away, or trade in your Mac - Apple Support

click on it.

wong2568 wrote:

I am going to trade in my macbook

Ok. That is nice. Do you have another question?

The instructions are at the link I provided in my post above. What is the issue you are having when following those instructions?