If you forgot your Apple Account primary email address or phone number - Apple Support
If you forgot your Apple Account password - Apple Support
If you cannot recover your old account using these support links you are out of luck, period. This is yet another example of why users should not typically change their Apple ID/Account. Your entire existence in the ecosystem is tied to your Apple Account, music, movies, apps, subscriptions, the list goes on. So why did you switch Apple IDs to begin with and why did you not write down and save the credentials for your previous Apple ID?
Besides that the App Store does not and has never kept records of hardware purchases, just software, apps, and subscriptions.
Your hardware purchases and warranty status are found at the following link.
My Support - Official Apple Support
Of course you’ll still need your previous Apple ID credentials to login.