retune
verb
re·tune (ˌ)rē-ˈtün 
-ˈtyün
retuned; retuning
transitive verb
: to tune (something) again or in a different way
retune an engine
especially : to readjust (something) in musical pitch
a guitar/string that constantly needs to be retuned
She retuned the banjo to G major.
Word History
First Known Use
1606, in the meaning defined above