automatically change all cell values based on updated entry

I need help:

How to do this:
If I change any value on column C, then it will automatically change all cell value on column C with the updated value based on same criteria on column B

like I have column b12 value as Test a then I change the value on c12 from 20 to 23, how to make automatic change on all value on c which have same criteria with b12 to the updated value (23)??

please help

Thank you