Find/Change long text

If I have very large text file

***************
***************
***************
***************
***************
ABC-sdfsdf
BBB-xk[ptr';
CCC-sdfolb
ABC-dltg'fl;l

My aim:
-> tail last 10 lines from large text. ***** Ok *****
-> Change first 3 charactors which begin with "ABC" to "abc". ***** ??? ****
Thk very much

Try this

tail -10 input_file | sed 's/^ABC/abc/' > output_file

Jean-Pierre.