Can't find "setting -> iTunes & app store -> password settings" on iPhone
From article Manage your iTunes Store and App Store password preferences:

Touch ID or Face ID will always override whatever preference you set.

So first turn off Touch ID for iTunes by:
Settings -&gt; Touch ID &amp; Passcode -&gt; Turnoff Touch ID for App Store.
Then go to Settings -&gt; iTunes &amp; App Store -&gt; Password Settings.