I want to handle press event with volume button up/down for increment and decrement counter in my app so is it feasible and apple will approve app ?
Volume Button Functionality
You are not authorised to disrupt the normal operation of those buttons. As per guidelines:
2.5.3 Apps that transmit viruses, files, computer code, or programs that may harm or disrupt the normal operation of the operating system and/or hardware features, including Push Notifications and Game Center, will be rejected.
Which means, if you intend to use for counting and cancel the volume up/down action, your app could (should) be rejected. So you cannot restore the volume level after using for the counter. If you don't perturbate that could be accepted. But you should explain it in your submission.
In a word, that's a risky design.