Open the design in Fusion 360
Go to the Solid workspace
Select the bodies or components you want to thicken
Click Modify
Choose Thicken
Select the wall faces or surface bodies
Enter the thickness value
Choose the direction for thickening
Click OK
Repeat for any remaining walls if needed
Use Press Pull if Thicken is not available for a specific face
Use Shell if you want to create uniform wall thickness from a solid body
Edit the feature in the timeline to change thickness later