My ex mygive me this phone but she forget password iCloud so how I am clean this????

Ask her:

See this Apple article: If you forgot your Apple ID password

If you forgot your Apple ID password - Apple Support

Then see this Apple article: What to do after you change your Apple ID or password

What to do after you change your Apple ID or password - Apple Support

Or see -> If you can't connect or sign in to iCloud

If you can't connect or sign in to iCloud - Apple Support

Looks like you have run into the Activation Lock where you need the password of the Apple ID that the iPhone is registered to. You are not going to be able to use this iPhone without entering the right password.

My recommendation is that you take your ex, your iPhone and the proof of purchase of that iPhone to the Apple Store or contact 👉 Apple Support to remove the Activation Lock.

Axel F.

How to remove Activation Lock - Apple Support