Start with tightening the lower chassis screws to see if the issue goes away, since it’s least invasive. That said, it can also be the screws inside the LCD assembly, but the issue is the procedure to tighten those is more invasive, and you need to be careful to avoid damaging the LCD - and watch for tape around the frame that’s used to secure it inside.
In most cases, I’ve also noticed it’s usually caused by the lower chassis screws, so the invasive option is not always needed. Refer to this guide to get to the screws for the hinges. However, if you continue to have issues then it usually is within the LCD assembly. You will need to work slowly if this is needed
If neither of these fixes help, then the hinges are worn out or the plastic broke somewhere. Chromebooks are inherently cheaply built, so it happens more than you think. The problem is shared on "enterprise" or "education" versions too, with the only difference being a bundled management license.