fill in vs instruct

fill in

verb
  • To inform somebody, especially to supply someone missing or missed information. 

  • To substitute for somebody or something. 

  • To complete a form or questionnaire with requested information. 

  • To beat up; to physically assault. 

  • To fill; to replace material that is absent or has been removed. 

instruct

verb
  • To tell (someone) what they must or should do. 

  • To teach by giving instructions. 

How often have the words fill in and instruct occurred in a corpus of books? (source: Google Ngram Viewer )