Digits to Letters

If you're talking about the passcode to unlock your device, you (or someone else, who knew your existing passcode) has changed the standard passcode (6 numbers), switching to a custom alphanumeric code (see the section "Change your passcode or passcode settings" in this support article:--> Use a passcode with your iPhone, iPad, or iPod touch - Apple Support ).

Since the passcode is stored inside your device, nobody here knows it. Neither we, just users like you, nor Apple can help you change it (unless you know the new alphanumeric passcode), we can just offer you the suggestions to remove it.

See these instructions, keeping in mind that if you don't have a backup all data will be lost on that device (except those that you eventually synced to iCloud):

If your device is running iOS 15.2/iPadOS 15.2 or later, AND if you have created a backup to iCloud, you don't need a computer:--> How to reset your iPhone, iPad, or iPod touch when you forgot your passcode - Apple Support

Shouldn't be this case (iOS/iPadOS earlier than 15.2), you need a computer. If you don't have a computer, borrow one from your friends/relatives/neighbors or ask for help at an Apple Store or Authorized Service Provider, then read these suggestions.

Given that to remove the existing passcode you must connect your device via USB to a computer (a Windows PC running the latest iTunes version, or a Mac, which can run iTunes or Finder, depending on the macOS installed on it), pay attention to the specific gestures that you need to perform while connecting your device to the computer.

These are the instructions to re-gain access to your iPhone/iPad:

If it is an iPhone:--> If you forgot your iPhone passcode - Apple Support

If it is an iPad:--> If you forgot your iPad passcode - Apple Support

Also, take a look at this support video about the same matter (for both iPhone and iPad):

https://www.youtube.com/watch?v=7s8-zLG9ySQ

Regards

Giulio