If you’re referring to the House of Representatives, single-member districts is a federal law, not a constitutional requirement. Congress could simply pass another law changing the old one, no constitutional amendment required. The method of representation in the Senate is codified fairly narrowly into the Constitution, but the House requirements are more lax and doesn’t forbid multi-seat representation. Technically the federal law allows for it too, but only if your state is grandfathered in. I’m not sure when the bill was passed or why that specific exception was put in.
If you’re talking about lower levels, multi-seat representation happens at the local level all the time. There’s a few states that have at-large districts in their legislatures, but single-member is way more common.
That’s fine if you don’t want to respond, I just want to make sure people reading have an opportunity to follow these links and realize that we do have plenty of multi-winner elections in the US.