Change Sets Limitations
Smart CPQ Quote and Smart CPQ Quote Line objects are part of the CPQ managed package and therefore cannot be included into a ChangeSet.
It is possible to include all entities managed outside of the managed package into a Change Set: Custom fields, triggers, and page layouts.
Note: For page layouts, good practice is to create a new layout for Smart CPQ Quote and Smart CPQ Quote Line instead of modifying the one from the managed package: These new layouts are then eligible for outbound change sets.