Prior to implementing the design, you must add any necessary design constraints to your project.
The constraints file for the block design are added to the project when you add the block design to the netlist project; however, if you have changed the hierarchy of the block design, then you must modify the constraints in the XDC file to ensure that hierarchical paths used in the constraints have the proper design scope. For more information, see this link in the Vivado Design Suite User Guide: Using Constraints (UG903).
A constraints file can be added to the project at the time it is created, as discussed previously, or right-click in the Sources window and choose Add Sources.