How to delete an email account on iOS and why you don't see a delete button.

To do a normal deletion for an , say, email account, just do:
settings -> accounts and passwords -> tap your account you want to delete -> tap delete.

If there's no delete button, you need to delete the corresponding profile by:
settings -> General -> Profiles 
to delete.

More information can be found here:
https://www.wikihow.tech/Remove-an-Email-Account-from-an-iPhone