If amount of GHs is decreasing i have to hire technician or i can fix it by myself? and is it difficult?
You have to hire a technician to do the job for you, you can't fix it your self...You could also rent a technician from the employee market for an hour to do the work with a lot lesser fee than buying a technician...it's very easy, upon repair, the miner will be switched off, so when the repair is finished, all you have to do is to resume the miner
To clarify, you need to buy or rent a tech, THEN go into your repair room and set him to repair a machine. THEN go into inventory when it's done and turn it back on.