I have a customer who started doing jobs for me can I also add him as a contractor

Welcome to the Community, @figueroastranspo.

Yes. You can add your customer as a contractor as well in your QuickBooks Online (QBO). To do that, you'll have to enter a name that is not exactly the same as the customer name, since QuickBooks doesn't allow you to enter the same name.

Here's how:

1. Click Workers from the left menu, then select Contractors.
2. On the Contractors page, click Add a contractor.
3. Enter the name in the field. (For example, if you set up your customer's name as Mark, you can enter Mark C as the contractor's name). 
4. Fill out the contractor's email address, then click Add contractor.

I'm adding this article for more details: Add, edit and inactivate contractors.

Just in case you want to invite your contractor to add their own 1099 tax info, feel free to check out this article for the detailed steps and information: Invite a contractor to add their own 1099 tax info.

Please know you can continue to reach me here with any additional questions. Thanks for coming to the Community, wishing you continued success.