My iPhone 6 is stolen and I want it to be diasabled. Please help me out. I am from karachi pakistan

If your iPhone has been stolen, report this to your Cellular Provider - as only they can block/blacklist the IMEI. Apple can’t help you with this process.

Here is Apple’s advice for lost or stolen devices:

If your iPhone, iPad or iPod touch is lost or stolen – Apple Support

Use the Find My app to locate a lost or stolen device – Apple Support

If the Find My iPhone feature was enabled prior to it being “misplaced”, then if active, you would stand a good chance of locating and managing it. 

However, if the feature was not activated prior to being misplaced - or the iPad has been inactive for more than 24 hours, the last known location will not be available - and the opportunity to use technical means to recover or manage the iPhone may have been lost.

If Find My iPhone or Find My iPad isn't enabled on your missing device - Apple Support

Apple cannot disable the phone. With no passcode on the phone, it would not matter if Find My was enabled or not.

The thief has complete control of the phone and the data on the phone. You need to protect your financial and personal information immediately.

Hello again ~ Take a look at this portion of the link you came from…

*But you can still protect your account if Find My was not turned on.

~Katana-San~

Hello ~ Work back three the link you came from. Did you have Find My activated?

~Katana-San~

Ansrooj wrote:

How can I disable my phone via IMEI or serial number??

If your iPhone is stolen that cannot be disabled using IMEI or Serial number.

You can use IMEI and Serial to file a complaint with the local law enforcement authorities. They will need both IMEI and the serial number.