Automated tracking requirements change

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C#

when your requirments has changed,we usually find the code and modify the source code by ourselves.
now,t have a question:
how to track the requirments changes autom Automation？
for example:
first you should establish the link between the requirment with the code,
when a requirment is changed,how can you trace the code that influenced by the change automation?


you can give some idea, thanks!