forgot apple keychain

If you forgot or don't know your old keychain password the solution is to create a new login keychain .As this sentence is written in this article : If your Mac keeps asking for the login keychain password - Apple Support

So , you can create a new keychain by following the steps as per the article : Change or reset the password of a macOS user account - Apple Support

In the last paragraph a method is shown create a new login keychain .

1. Open Keychain Access, which is in the Utilities folder of your Applications folder.
2. Choose Preferences from the Keychain Access menu, then click the Reset My Default Keychain button in the preferences window. After you enter your new password, Keychain Access creates an empty login keychain with no password. Click OK to confirm.
   If you don't see a Reset My Default keychain button, close the preferences window and select the “login” keychain from the left side of the Keychain Access window. Press the Delete key, then click Delete References.
   
3. Choose Log Out from the Apple menu to return to the login screen.
4. Log in to your account using your new password. Your account password and login keychain password now match again.

Hi there,

You might try to turn off the keychain in iCloud setting, and turn it on again. Then, you might see the forget button.