I would like to remove apple id that's not mine.

I see you say this was done on a computer so how you proceed may differ from where we usually see this which is on a mobile device.

Sign out of iCloud on your iPhone, iPad, iPod touch, Apple TV, or

Mac --> https://support.apple.com/HT208242

If your son created a new user account to do this, you can always delete the entire user account from an administrator account.

Delete a user or group on Mac - Apple Support

YOu will have to enter the ID and password used to lock it. If you can't do that, as long as you are the original owner and can produce legitimate proof that you are the owner (which must include the serial, IMEI or MEID number) you can request unlocking as detailed here: Activation Lock - Support. Note that the process will completely erase the device.