to return to a previous situation, form, etc.; to take off your clothes and put on what you were wearing earlier
change back (into sb / sth)
to return to a previous situation, form, etc.
change back (into sth)
to take off your clothes and put on what you were wearing earlier
She changed back into her work clothes.
change sth back (into sth)
to exchange an amount of money into the currency that it was in before
You can change back unused dollars into pounds at the bank.
Definitions from the Oxford Advanced Learner's Dictionary, 9th edition