1
general::
Alternate, or take turns. This phrase is used either for two individuals alternately performing a task, as in Lifting cement blocks is such heavy work that they decided to change off periodically, or for one person alternately performing two tasks, as in I can concentrate on this book only for short periods so I frequently change off and work in the garden. Also see CHANGE OF PACE.
American Heritage Idioms
2
general::
Phrase(s): change off
[for people] to alternate in doing something. • Tom and I changed off so neither of us had to answer the phone all the time. • Let’s change off every 30 minutes.
McGrawhill's American Idioms And Phrasal Verbs