I have a new phone with new Apple ID and I’m trying to connect the old with the new one but that other phone is lost but I still remember my password

but that other phone is lost but I still remember my password

Check the Apple ID of the other phone via your email box, see this Apple article: If you forgot your Apple ID

If you forgot your Apple ID email address or phone number - Apple Support                  

OR see -> Having trouble signing in?

https://iforgot.apple.com/password/verify/appleid

FYI: Your Apple ID is the personal account you use with all Apple products and services. It includes the email address and password you use to sign in, as well as the contact, payment, and security details that you use with Apple.

👉 You can’t merge multiple Apple ID accounts.