Thanks for the photos, So teh first thing is that since you are using a brushless gimbal, the controller itself takes care of the stabilization, and you simply need to setup a pass-through on your CC3D from your receiver in order to manually adjust the pitch angle.
The easiest way to get this working would be to bypass cc3d entirely, so all you need to do is figure out which channel on your flight controller corresponds the the switch/knob you want to use for pitch control (most likely channel 6). Then you just need to take a wire from CH6 on your receiver and connect it directly to the pitch input pin on your gimbal controller (the red one you circled)
The only reason to pass the pitch control though your autopilot would be if it has something like a point of interest/ follow me feature where the flight controller will adjust the pitch depending on your altitude/distance to keep you in the frame. IE when you the drone is directly above you the gimbal will pitch down, and as it moves further away, it will pitch up. If this is the way you want to connect it, you will need to connect the gimbal signal to a spare output on your CC3D Board, in the example below I connected it to output 6.
You will then need to setup and configure the CC3D software to tell it that gimbal pitch control is read from ch 6 on your receiver, and will output on output 6 (the actual channels might vary depending on your R/C system). I cant give too much information on how to do this as I dont have it installed on my PC right now as I am currently traveling, but if you need help with this just let me know and I will be able to get write a better tutorial on Monday when I am back at work.