How do I change my business code on the turbotax return to 721191 to reflect my category of Accomodation/Bed and Breakfast? Thanks You

If you have not filed your return just revisit your schedule C and follow the interview until you reach 'Let's look up your business code' then make the correction.

If you have already filed, you would need to file an amended return to correct it, however generally you would not file an extension to correct only this error. 

You do not have to change the business code if you accidentally used the wrong code.  Business codes are used by the IRS to categorize your business for statistical purposes only. The code you enter will not affect the outcome of your tax return.  The code does not have any impact in your tax return it is used for statical purposes.  However, it is always best to have all your information correct. The link below has information you may find useful.