What the viewmodel commands do
The viewmodel is the weapon you see in first person. viewmodel_fov changes how large it looks, with a range from 54 to 68 in CS2. A higher value pushes the gun toward the edge of the screen and shows more of the map around the crosshair. viewmodel_offset_x moves it left or right (range -2.5 to 2.5), viewmodel_offset_y moves it forward or back, and viewmodel_offset_z moves it up or down (both -2 to 2).
How to apply it
Open the developer console (enable it in Settings, Game, Enable Developer Console, then press the key you set, usually the tilde key). Paste the one-line command and press Enter. To keep the values after a restart, put the config lines in your autoexec.cfg file. Setting offsets by hand overrides the built-in viewmodel_presetpos presets, which are Desktop (1), Couch (2) and Classic (3).
How to choose values
A small, low gun leaves more of the screen free, which many players like for long angles. A larger gun at the side can feel easier to track while moving. The starting points above are common patterns, not official presets and not any pro player's exact setup. Try a value for a few deathmatch rounds before you judge it. For pro examples, open a profile in our players section and compare with the source linked there.