I have mild pain on my right knee and only happens during intensive running. I dont feel pain when walking. How to treat this pain?

Varies. If you aren't having a lot of trouble, one person might just adjust their exercises to avoid aggravating it; such as trying to go from running to biking for example. Trying an anti-inflmatory medication could potentially help as we as appropriate warm up and stretching. If it is problematic enough, consider being seen for an exam and studies for a specific diagnosis for further treatment options.