How do I add touch passwords?

You will likely need to contact support for the App itself.. Apple is not the one that designs the apps to use Touch ID. The developer that designed the app would need to integrate it.

Out of curiosity, what is the app?

What are you calling 'touch passwords'?

Do you mean the iPad remembering your passwords and using your fingerprint to auto-fill the passwords? (Keychain)

Use Touch ID on iPhone and iPad - Apple Support

Set up iCloud Keychain - Apple Support

Do you mean Touch ID? There is no password for that just your fingerprint(s).