Bought used iPad and not able to unlock it

i couldn't find him, now i cant find him...how can i fix this issue

Buy purchasing a new device from an authorised Apple reseller or an Apple store. The devices you have are useless to you if you can't unlock them.

See

Activation Lock for iPhone, iPad, and iPod touch

How to remove Activation Lock

Follow the onscreen steps to enter the Apple ID and password you used to set up your device or your device passcode.

Is the iPad disabled or Activation Locked? If so, unless you can independently obtain assistance from the previous owner, the iPad is (and will remain) useless to you.

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

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 sales receipt showing the serial number), Apple may be prepared to assist - otherwise they and nobody here will be able to help you.

The All Too Common SAD Reality of Buying … - Apple Community

Here is what Apple suggests when purchasing used:

Check for Activation Lock before you buy a device from someone else

Before you buy an iPhone, iPad, or iPod touch, from someone other than Apple or an authorized Apple reseller, make sure that the device is erased and no longer linked to the previous owner’s account. Follow these steps to check if the device is ready to use: 

1. Turn on and unlock the device. 
2. If the passcode lock screen or the Home screen appears, the device hasn't been erased. Ask the seller to completely erase the device by going to Settings > General > Reset > Erase All Content and Settings. Don't take ownership of any used iPhone, iPad, or iPod touch until it's been erased.
3. Begin the device setup process.
4. If you're asked for the previous owner’s Apple ID and password, the device is still linked to their account. Hand the device back to the seller and ask them to enter their password. If the previous owner isn't present, contact them as soon as possible and ask them to use a browser to remove the device from their account. Don't take ownership of any used iPhone, iPad, or iPod touch until it has been removed from the previous owner’s account.

You will know that a device is ready for you to use when you're asked to "Set up your iPhone," “Set up your iPad," or “Set up your iPod” the first time you turn it on.

You can't, only the original owner can remove the activation lock. If you can't find the guy you bought it from then it's completely useless to you, the only thing you can do with it now is recycle it. If it was "very cheap" then my hunch would be that it wasn't his to sell (ie you're now in possession of stolen goods).

Anyway, there's absolutely nothing you can do to make it usable.

I hate to break it to you, but you purchased what are almost certainly STOLEN goods.