ipad 1st generation. forgotten password and disabled. How can I reset?

You’ll need access to either a PC (with iTunes installed) or a Mac (with iTunes or Finder - as appropriate for the installed version of MacOS).

You’ll also need your AppleID and associated password. If these have also been forgotten, they can be recovered here:

https://iforgot.apple.com

To recover your credentials, you’ll need access to one of the following:

• Your primary email address mailbox that corresponds with your AppleID
• Any of the secondary/recovery email addresses that should be configured for your AppleID account
• Any of the trusted telephone numbers (fixed line or Cellular/Mobile) that are associated with your AppleID

Unless you AppleID account has not been fully/correctly configured, or has been seriously neglected, recovery of the AppleID and password should not be difficult.

More information about recovery of your AppleID:

If you forgot your Apple ID - Apple Support

More information about recovery of your AppleID password:

If you forgot your Apple ID password - Apple Support

When you recover access to your credentials, you would be well advised to log-in to your AppleID account from a web browser - and verify/update any email addresses and trusted telephone numbers:

https://appleid.apple.com

You will have to restore it using a computer. The process will erase the device. Later you can restore your data with a recent back-up. Instructions here...

If you forgot the passcode on your iPad, or your iPad is disabled - Apple Support

If you do not have a recent back-up, you will find the 1st generation iPadvirtually useless. It is an antique and does not have the components necessary to run today's apps.

The reset will erase everything off this nearly 11-year old iPad.

While you will find restored iOS 5.1.1 apps installed at reset, that default Safari Web browser is far too old to ever be trusted on the Internet, any longer, in 2021.

Also, there are virtually NO MORE iOS App Store, third party apps available for that old an iPad, any longer, making this nearly 11-year old iPad pretty much a useless, obsolete device now.

Without access to old iTunes backups, where older apps could be stored and saved, this old iPad model is done.

Your iPad is too old for any iOS upgrades/updates, either!

Sorry.

Just forget about this old iPad, now.

You really need to seriously consider a new iPad model OR a much, MUCH “newer” and less expensive, used iPad models, from better known, trusted Apple product/device retailers/resellers, capable of running the latest iPadOS versions.

A WHOLE LOT has happened with iPad/iOS in the past 11 years since this first iPad was introduced.

There are plenty of newer, older iPad models that can run the latest, current versions of iPadOS.

Sorry & Best of Luck to You!