How can I open this monitor?

Most modern monitors are snapped shut and don’t use screws outside of the stand. The issue is knowing which way to work. Many of the modern ones come apart starting with the bezel, but some like the Dells are assembled from the front. I would go from the back first to be safe since that’s the more typical way of doing it.

Once you know which way to work, start from the bottom and start removing the snaps. If you have to use harsh tools, work from the bottom to avoid deep visible gouges. Once you have one side unsnapped, do the same for the other 3.

After you get at least 3 sides loose, then you can typically work the final side off by hand on the final side with some caution. If it’s stubborn or edge to edge, it’s best to work all 4 sides off before removing the front or back bezel. I would expect a little cosmetic damage will be done to the monitor since you really can’t avoid it.

This can be difficult to do, especially if it hasn’t been opened by a previous owner. As long as you keep this in mind, you’re not going to break anything as long as you're careful.