How to test fuel gauge onboard

[j1w1]

I would like to know how I can see what my fuel capacity is on my dashboard screen, other forums talk about doing the dashboard number 6 test. I push the two levers on by dashboard and hold them in for about 5 seconds. A test menu pops up and there are 22 test modes, when I scroll to test number 6 and push the button, then it says locked. Must you have a computer connected to the car or can someone tell me what buttons to use in order to toggle the settings and to activate test number 6.