in hand / at hand

• at hand

you have something conveniently near you
e.g. Make sure that the safety equipment is at hand when you start working, in case there are any problems.
e.g. I do not have Dominic's telephone at hand, so I will tell you later.

• to hand (can be used the same as 'at hand')

e.g. I am sorry I haven't got the information to hand, can I tell you later?

• in hand

1. if you have something in hand, then you have extra amount, or you have more than you need. we may use this talk about time.
e.g. I am not worry about finishing this essay before the deadline, since I still have 3 days in hand.
2. the, job, situation, problem or topic that you are dealing with at the moment can be described as the problem in hand.
e.g. At the moment, the problem in hand is how to motivate yourself start working.
3. if you want to say that you are in control of a difficult situation, you can say that you have this situation in hand.
e.g. Do't worry about the preparation for the party, I've got everything in hand.

Reference