Talk to them and figure out what's different between your team and their previous team. You might be able to change things to get more from them. If not, let them move on to another team where they can be better.
Pretty soon after I started, it dawned on me that I would probably not partake in designing "the big" stuff. Partly because most of the big stuff was already done and whatever remained would probably be solved by some of the more senior devs. Any semi-large stuff would need to be fought over by the rest of the devs. What was left was drudge-work compared to all I had done before. Also most of my tech-skills (besides the programming language in question) were not needed and when I helped a colleague in another team working on something I knew pretty well, my manager reprimanded me after, telling me that our team couldn't spare the 2hrs I spent.
I was pretty unhappy and during this time was pretty far from living up to my own expectations. My manager never told me I was falling behind however so I don't know about their expectations. I quit soon after.
In my case I was moving from the experience of small companies and being "forced" to do everything, to a large company and only allowed to do very few things.
Read the book Difficult Conversations.
From the book, you need to prep by looking at the situation from your perspective and the other person’s. This has been very helpful for me in figuring out these tough situations. Then you look for the difference in those stories, hear the other person’s story from their perspective and work towards a solution.
Generally the more you put off these conversations the more you’ll regret it. And honestly it’s a weight off your shoulders when you do have them and you’ll often wish you had them sooner.
And most people in my experience hate starting these kinds of conversations so more often than not, in some way, they appreciate that you as their boss are starting it for them.
I've seen this at work with a Managing Director and her direct reports. Direct reports to a Managing Director are hyper competitive and cutthroat. Think of them like the velociraptors in Jurassic World, if you can keep them focused and not killing each other or everyone around them they're a very powerful force. This MD would just hand out verbal "gold stars" on an all hands call. The DRs would get noticeably upset when they did not get the "gold star".
In that context you could ask again if there are any issues they have or if there are any challenges they face that might make this difficult etc.
This way you can get your message through without it becoming confrontational or the other person getting overly defensive.
Also, understand that the new person is learning the context and team culture, and will take some time to get up to speed. How long have they been on the team? How long have you been on the team? The other team members?
There is a lot of context to consider. We can make a lot of assumptions based on our own experiences, but may end up sending you astray.