Hi Sonyad77,
Welcome to Apple Support Communities. Usually trust certificates are installed with a profile such as from a school, business or organization as mentioned in Trust manually installed certificate profiles in iOS and iPadOS - Apple Support.
You might be able to remove the profile using this guidance from Install or remove configuration profiles on iPhone - Apple Support.
"Configuration profiles define settings for using iPhone with corporate or school networks or accounts. You might be asked to install a configuration profile that was sent to you in an email, or one that’s downloaded from a webpage. You’re asked for permission to install the profile and, when you open the file, information about what it contains is displayed. You can see the profiles you have installed in Settings > General > VPN & Device Management. If you delete a profile, all of the settings, apps, and data associated with the profile are also deleted."
Kind regards.