I did every possible way that i could learn from the internet but could not make it possible.
My unity Version is Unity 2020.1.1 I also have tried this way from this website (Basic ads integration for Unity developers | Advertisement | 3.6.1 (unity3d.com)) but could not get it over and it does not works… and for youtube video it is from here (How To Monetize Your Game - Unity Ads Tutorial [2020] - YouTube)
We have a bigger guide available here, which you might find useful 
https://unityads.unity3d.com/help/unity/integration-guide-unity
Thank You Sir @ kyle-unity … I am grateful to you…