How can I access my Apple ID password that I have forgotten a month ago?

You are sign in here .  .  .  with your Apple ID & Password (?).

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.

Check your Apple ID 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

See also -> If you can't connect or sign in to iCloud

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

How do I connect my Apple phone with other devices?

See -> Check your Apple ID device list to see where you're signed in

Check your Apple ID device list to see where you're signed in - Apple Support

• Add the iPhone to your account.

See also -> View and remove your devices that are associated with Apple ID purchases

View and remove your devices that are associated with Apple ID purchases - Apple Support

Manage the list of devices that can download and play items that you bought with your Apple ID.