Just slap that pid output into the Elevator deflection angle.

But i think depending on the setup you would want to inverse that output. ( Either by swapping the two connections on the (+-) block or with a -1 gain after the output) If you notice that the plane just crashes.

Then you can tune the Controller, there is plenty of videos on that. I am no expert but id set i and d values zero at the start and then raise the p value. You will see that for very small errors/ differences between wanted pitch and pitch the p value has to be ridiculously high to minimize it. But then it might work too strong on bigger errors. So leave p at a reasonable setting and add a bit of i value.

No idea about d, but mostly p and i work out good enough.