Movement in head tube/fork?
The tube you’ve circled is the head tube. Inside the tube, on the top and bottom are the headset bearings which allow your fork to turn smoothly.
The bearing play or preload has to be set correctly with the vertical screw on top of the stem cap.
If there is play in the bearings allowing the fork to rock back and forth you’ll have to adjust the preload. To do that you have to loosen the two screws on the left and right side of the stem which clamp the stem to the steerer tube. Then slightly tighten the vertical screw until the play is gone. You shouldn’t need force, we are talking &lt;2Nm torque here. The fork should still turn freely, if it doesn’t you’ve tightened too much. Afterwards, make sure the stem and handlebar are aligned correctly to the wheel and tighten the two screws to the left and right.
See this tutorial: https://www.pinkbike.com/news/tech-tuesday-headset-adjusting-2010.html
Since you have carbon components you should use a torque wrench to tighten to the specified torque.
If the steering feels rough the bearings are worn and have to be replaced. If you suspect bearing damage it could also be a good idea to completely remove the fork and take a look at the bearings directly and how smoothly they run.