Should be easy to find. A novel. Read it in early '00s. More likely it is much older. It might be a series of novels.
A fleet of traders traveling through space from star to star. They trade technologies.
The captain of this fleet is more likely from Earth, he's mostly immortal cause he bought some medical tech on one planet.
The plot of one book was that the captain has been captured and imprisoned on his flagship.
He managed to regain the control of his fleet using some spec-of-dust-sized robots flying all over the ship and doing some maintenance, by grabbing a couple of these robots into his eye.