I can't remember the Passcode to My previous iPad, now I have an iPhone I keep getting message that says approve iphone from another decide. I don't know what to do.

Hello amakafromlag,

You can use these steps to restore the iPad to factory settings, then try setting up the iPhone again:

1. For  iPadOS 15.2 or later, see steps in: If you see an iPhone or iPad unavailable message or Security Lockout screen For earlier versions, follow these steps instead: If you forgot your iPad passcode (Computer required.)
2. After this, you'll need to set up the iPad: Set up your iPhone or iPad (Associating it with your Apple ID.)

If you're then unable to restart and approve the iPhone, then you'll need to Reset Encrypted Data. Which means, that you'll lose passwords saved in iCloud Keychain. Then it should allow you to proceed. Keep in mind, this does result in data loss for iCloud Keychain. However, it will create a new iCloud Keychain for you moving forward.

Let us know if this helps out, take care.