Hi,
Follow below steps:
1. Retrieve an assembly, select a part, and click Edit > Activate.
Note: The Merge feature will be created in the selected part.
2. Select a second part in the assembly as the reference model from which geometry will be copied and click Insert > Shared Data > Merge/Inheritance. The Merge dashboard appears with the reference model selected by default. You can replace the reference model by selecting a different part from the Model Tree or graphics window.
3. Define the Merge feature properties as follows:
—Add (default) or remove material geometry.
—Set reference type to assembly context (default).
—Set reference type to external (create an external Merge feature).
Click References to define the following options:
Edit—Control propagation of annotation features.
Copy Datums—Toggle datum copying from the original feature to the Merge feature.
Note: You can copy datums only if the Dependent option is active. If the feature is independent, no datums are copied. Datums may be refited with existing geometry only.
Click Options to define the following:
Dependent—Make the Merge feature dependent (default) or independent of the reference model. Dependent features update when changes are made in the reference part. An independent Merge feature will not update when the reference part is modified.
Note: If a Merge feature is independent, you cannot externalize the feature.
Click Properties to change Merge feature name.
Hope this is helpful.