Issues with team memmber

The Scrum Master does nothing.  That is up to the Developers and the Product Owner to discuss and decide a course of action. 

Colleagues have a question, what would you advise scrum master to do if one of the developers did not finished the task for the sprint, told about it by the end of the sprint and deleverie had to move.

What should the scrum master do in such cases?
What techniques should be used to avoid such cases in the future?

The accountability is called Developers, and not Developer, for a reason. The Developers are jointly accountable for ensuring that their commitments are met. If there's any policing to be done they ought to police themselves. A Scrum Master might possibly reveal that truth.

Could you please explain in step-by-step mode.

I'm afraid not. Scrum is based on accountabilities and commitments, for which collaboration and empiricism are required. Oftentimes it's reductive step-by-step thinking which causes problems in the first place.

Thanks for your comments.

Ofcourse the accountability lies with the Developer, to stand to his estimates, however there can be reasons for the task which is still not done. SM can understand and facilitate a meeting with the PO and there they may come up with a priority plan and identify due course of action that needs to be implemented in the upcoming sprints.

I think  you guys need to talk about this. Maybe he's got some personal issues that affect his performance at work and he simple needs a hand with something. I think it should be discussed and he needs to get some moral support. Good luck with this.