I am not able to delete unverified certificates.

Okay, the error you’re reporting here is likely a subscribed calendar, the target domain for the subscribed calendar appears misconfigured, and this stuff is ~unrelated to the trust store, and the zz app stuff is another domain associated with the same domain that you’re having issues with. (There are a gazillion top-level domains like the familiar com, net, and org around, and app is one of the many others.)

go to to General Settings / Calendars / Accounts / Subscribed Calendars and check if there is any calendar subscription

1. Is this your corporate iPhone? Then please contact the system administrator of your corporate
2. If it is your personal device, in that case, do you have any profile installed by your corporate/organisation/enterprise/School Management?
   1. Erase the profile added by you If you have installed a profile on your own --> Install or remove configuration profiles on iPhone - Apple ...
   2. Or please contact the system administrator of the organisation who provided the profile to you