See if you can recover the old password. If you forgot the Apple ID (iCloud) password, enter the Apple (iCloud) ID, and click Forgot Password. See if you can get a Rescue or Notification email option if necessary. Link to contact Apple Support at the end of the 2nd article.
Apple ID - Manage
Apple ID – Forgot Password *
If you have 2 Factor Authentication enabled, if you can't recover the password using the steps above, you will need to use Account Recovery. The Recovery Process is an automated process and the length of time it takes can vary a lot. Apple ID Support can only answer your questions. They can't intervene in or speed up the process. The article below has some suggestions to shorten the time the process takes.
Apple ID - Recover your Apple ID with two-factor authentication account recovery. *
If you can't recover the password, if you weren't syncing with iCloud, do you have a backup you can restore from? Restoring from a backup erases all data currently on your device. Any data newer then when the backup was made will be erased. A restore is an all or nothing restore. You can't access a backup to see the contents and only restore certain files.
Backup - Restore your device from an iCloud or iTunes backup. *
ASC YouTube for how to restore an iPhone, iPad, or iPod touch from an iCloud backup
ASC YouTube for how to restore your iPhone or iPad from a backup on your Mac