an old hand
One who has experience doing a particular task. If you have any questions, ask Andrea—she's done this job before and is an old hand at filing. I've been a bus driver for seven years, so I'm an old hand at this.
old hand (at doing something)
someone who is experienced at doing something. The maid was an old hand at polishing silver. Bob is an old hand at training dogs.
old hand
verbSee old hand at something