Screens get dirty in a shop. They can also get easily be damaged. Then even a tiny flaw on the screen stands out.

For deep cleaning, you need some household or commercial grade disinfectant that states on the label it is viricidal or listed with specific COVID-19 claims. So first wet a microfibre cloth. Now wipe the screen with this damp cloth. Do not use force.  Now wipe with a dry microfibre cloth.

But do not clean the monitor while it is on as it is hot. Let it cool down. A good time to do it is in the morning before you start it up. What can happen is the evaporation of the cleaning material can cause streaks.