I received Releve 1 from Revenu Quebec with 800$ under box O but there is no such a box in turbo tax. Many thanks in advance for the help.

On the Releve 1 entry page, if you scroll down the page, in the left column it says, "Amended Slip?". Under that is the title "Box O", and several different boxes with letters (RN, RJ, RU, etc...). These are all Box O, and you would enter your amount in whichever box that matches the code in the “Code (case O)” box on your RL-1 slip.