How can I delete an Apple Account someone else set up on my iPhone?

Hello~ Did you share your credentials with someone? Explain without posting any personal or sensitive information. Do you have the original purchase receipt for your device? In the meantime click on below and review…

If you think your Apple Account has been compromised - Apple Support

~Katana-San~

I suggest you start by following the instructions in the two articles linked below:

Change your Apple Account password - Apple Support (CA)

Set a passcode on iPhone - Apple Support (CA)

Following the above will secure both your Apple Account and your iPhone.

I hope this has been helpful to you!

Cheers =)