You now know how to change the coordinate system for a map, and how to assign one to data that is missing a coordinate system. But how do you change the coordinate system for data? That process is called projecting data.
When you need to move or project data from one coordinate system to another, it requires a lot more than just redefining the assigned coordinate system like you did in the previous recipe. It requires ArcGIS Pro to recalculate all the coordinate values for the features within that dataset. This means all those features will have new coordinates that represent values in the coordinate system it has moved to. To calculate the new coordinate values, ArcGIS Pro must perform many calculations for each feature to account for possible changes in datums, units, reference locations, earth models, and more. So, it can take a long time for larger datasets.
The tool you use to move data from one coordinate system to another is the Project...