In the past I used a react UML library to create a react screen with drag n drop UML objects. There was a pallet that the user could drag and drop the different shapes on the screen, including the connectors, to manually build a UML diagram. I can't remember the name of that library. All of the libraries I've found so far generate the UML from code. Which is nice but requires a lot more work to recreate what I'm trying to build. The library I used had the drag and drop code already built in.
It's possible that the library you used was a custom-built solution or a less well-known library, so it may be helpful to review your code or project history to try to determine the specific library you used.
If none of these ring a bell or don't lead anywhere. Let me know if this helps or doesn't help