I am using a Microsoft Lumia 640XL, and double tap option automatically activated for all option with sound. i.e. for open screen say double tap; call say double tap
please help for unlocking the same.
Perhaps you are talking about the Narrator option which reads all the text on the screen and perform actions on double-taps. Assuming that, solution to your problem is Go to settings > double tap ease of access > double tap narrator > double tap the On button to turn it off. Now the narrator is off. To unlock your phone while narrator is on you have to double tap every number of your pin since single tap will only read that number aloud and will not allow you to enter the number. Hopefully I understood your problem well and hopefully it helps.
To deactivate the narrator you have to hold both the volume buttons and click the Windows icon on your screen and it will stop.