How can I sign out an unknown Apple ID and sign in with mine?

If this is a used device, the previous owner needs to go to https://www.icloud.com/find/ and erase the device, then remove it from their account. If they won't do that, the device is useless. Apple won't unlock it.

Turn off Activation Lock - Apple Support.   *

If you are the original owner, contact Apple. Apple can remove the ID  if provided the required paperwork to include the original purchase receipt with the serial number on it. 

Request additional support for unlocking your device.    -

You used to be able to take the device, the original purchase receipt with the serial number, and a photo ID to the nearest Apple Store (if it has reopened) and have them remove the ID. This may have changed, so call the store before going to make sure they can help.

Genius Bar Reservation and Apple Support Options - Apple.   -

Purchased used or second-hand? If so, I’d guess that somebody hacked around Activation Lock somehow, and the hack just stopped working. If that’s the case, this iPhone won’t be useful.

If you purchssed this iPhone new, you’ll need the original purchase receipt or similar proof of ownership, and a discussion directly with Apple.

In general…

Activation Lock is intended as a theft-deterrent mechanism. A theft deterrent that is easy to bypass would not be much of a deterrent.

Nobody here in the Apple Discussion Forums can help you clear Activation Lock.

To clear an Activation Lock, you will need the password of the associated Apple ID, or the original purchase receipt and a discussion with Apple Support, or similar proof of ownership.

If this device was recently purchased and the seller is still available, contact the seller for remediation or for refund. A remote unlock using iCloud is available to the person with the Apple ID holding the Activation Lock, if that person is still available and is inclined to unlock this device.

Again, only the person with the credentials to the Apple ID holding the lock, or Apple, can clear this lock. For Apple to clear the lock, you will have to provide a receipt with proof of original purchase and with matching serial number or IMEI, legal paperwork from an inheritance, or other similar proof of ownership materials.

For recovering access to your own Apple ID, if you are the holder of the Apple ID associated with the Activation Lock:

If you forgot your Apple ID password - Apple Support

If you forgot your Apple ID - Apple Support

How to use account recovery when you can’t reset your Apple ID password - Apple Support

Contact Apple for help with Apple ID account security - Apple Support

If you are the heir:

How to request access to a deceased family member's Apple accounts - Apple Support

Purchasing devices with Activation Lock is unfortunately far too common. These are scams, and other fraudulent sales. These locked devices will not be useful to you, and are probably best recycled. See the following link for more info:

The All Too Common SAD Reality of Buying a Used iPad/iPhone

If you can't contact your brother to see if it is his Apple ID, then get the ID/password so you can sign out, and you don't have the original purchase receipt, the phone is useless. Apple won't unlock it without a copy of the original purchase receipt.

sukhjit257 wrote:

phone is working no issues is accruing but i just want to use my own apple id for that i need solution and apple id and password has made by my brother. i made apple id in india when i got

Other than that the phone is showing as lost or stolen, or actually is lost or stolen, and that nobody here can help you bypass Activation Lock, sure.

Call Apple.