I have 2 self employed business listed in turbo tax and I would like to merge them into one business. How can I do this?

You would need to choose one of the Schedule C businesses to keep as part of your return and edit the Business Profile for that one to reflect the new joint business if any changes needed to be made.  

Then, take a look at any Assets being depreciated for the other Schedule C business and re-enter them under the business that you are keeping.  

Also, take a look for any vehicles being used for the business you are not keeping and enter it under the combined Schedule C if the vehicle is used for the combined business.  

Go through the Schedule C for the one you are not keeping on your return and be sure that everything has been transferred to the combined Schedule C before deleting the one you are not keeping.