We need to write a test cases/scripts for the new CR.
and we should test the CR independently.
And u link/merge with the existing 
product /code/application and check either any impacts on 
the existing things based on this CR.

When a CR's Arrives, all the following thinkgs are carried 
out step wise:
>>Walkthrough meeting where the business analyst explains 
the CR in detail to the developers and the testers
>>Review meeting carried by Testing team seperatly and 
assigning the CR to a particular candidate to find the 
impacted area due to this.
>>Candidate to write test cases and send across for review.
>>And as soon as the code is ready, carry out testing and 
keep the proofs for the defects raised.
>>Retesting for fixes if pass simultaneously carry out 
regression testing.
>>And once testing is stopped, it is delivered.

CR means Change Request.

 When CR come to the tester, managers will send the CR 
details with description.If you are not able to understand 
that, they will be  walkthrough.
 When CR come we need to write the test cases for that, and 
we need execute that.