Change the base of a topic branch

$ git rebase --onto staging develop topic

That will move use from this situation:

o---o---o---o  staging
 \
  o'--o'--o'--o'--o'  develop
		   \
 		    *---*---*  topic

To this situation:

o---o---o---o  staging
 \           \ 
  \           *---*---*  topic
   \
    o'--o'--o'--o'--o'  develop

See https://git-scm.com/docs/git-rebase