I don’t understand your problem.
You are trying to get a screen working direktly on the Pi or over HDMI?
I installed the official 7″ Touch on my Pi
Getting it working with an older Raspberry Pi Model „A“ or „B“
With the software updated it’s actually reasonably straight-forward to get the touchscreen working with a Model A or B Raspberry Pi. First you must make two additional connections between your Pi’s GPIO and the touchscreen: these are the SDA ( http://pinout.xyz/pinout/pin3_gpio2139 ) and SCL ( http://pinout.xyz/pinout/pin5_gpio376 ) lines ( which you can connect using the supplied green and yellow wires ).
Finally, you need to enable the LCD which is normally ignored on the main i2c bus:
Note: This will give your i2c over to the Pi for running the LCD/Touchscreen and you wont be able to use any other i2c devices or add-on boards which require i2c.