Open the design in Fusion 360
Go to the Solid workspace
Click Create
Select Mirror
Choose the mirror type:
Bodies
Features
Components
Select the body, feature, or component to mirror
Select the mirror plane
Click OK
Use Origin planes or a construction plane as the mirror plane
Create a construction plane if needed
Use Construct
Select the required plane type
Confirm the plane position
Repeat Mirror for additional geometry if needed
Save the design