Reset Passcode for iPad

Assuming that you can access your iPad:

Settings > TouchID/FaceID & Passcode > Change Passcode

If you are asking this question because you have forgotten your Passcode - and cannot access your iPad - then you’ll need to follow this:

https://support.apple.com/en-gb/HT204306

I hope this resolves your query.

See instructions in If you forgot the passcode for your iPhone, iPad, or iPod touch, or your device is disabled - Apple Support