Do you want to Format a second drive and NOT risk losing data on the FIRST drive? That is easy - it is the normal way things work. A Format is done ONLY on the drive you tell it to, not on ALL drives. So you must be careful to select the SECOND drive before issuing a Format command on it.
However, if you are asking how to Format the Second drive and not lose any data already on that SAME second drive, that is impossible. A Format wipes out all records of whatever data is on the drive and then re-writes several of the tracking files, so you cannot keep data on the same drive you are formatting.