How do I restore an iPad without a computer?

If by “found it” you mean it’s not actually yours then no, there is no scenario where you would be able to unlock it for your use. Only the true owner can. If it’s yours and you just can’t remember your passcode then you will have to follow the steps…you will have to find a computer to use.

If you forgot your iPad passcode, use your Mac or PC to reset it - Apple Support

Repeated entry of an incorrect device passcode will cause the device to become disabled - after which, the only remedy is to reset and restore the iPad using a Windows PC or Mac computer. Resetting the iPad will trigger an Activation Lock - that must be satisfied by the owner of the AppleID that last successfully activated the iPad.

If the iPad disabled or Activation Locked, unless you can independently obtain assistance from the previous owner, the iPad is (and will remain) useless to you. If you are able to contact the original owner, they will require this information:

What to do before you sell, give away, or trade in your iPhone or iPad - Apple Support

Here are the Apple support pages that outline the Activation Lock - and the only mechanisms by which it can be satisfied:

Activation Lock for iPhone, iPad, and iPod touch - Apple Support

Turn off Activation Lock – Apple Support

As you will discover, unless you are the owner of the AppleID that was last used to activate the device, you’ll not be able to defeat or bypass the Activation Lock. With documentary evidence that you are the original owner (such as the original sales receipt showing the serial number), Apple may be prepared to assist - otherwise they and nobody here will be able to help you.