Quality is delighting customers
1) Gauge the changes with Impact Analysis
2) Prepare a RTM to track the changes to closure and delivery
1a) If the change is a new requirement, analyze what caused this change
2a) If the change is a defect fix perform escape analysis
Rest of the stuff is BAU as in case of any other requirement like, plan, prepare tc, execute tc, track report defect...
If requirements are changed after project is signed off by QA , appropriate Change request should be raised and assigned to testing team.
Testing team should analyse the impact of the change and accordingly provide testing estimates , prepare test cases , execute and log defects
First of all prepare one change request document and identify which area or module affected by this changes.Send this document to all your team member and tell them to read it proper.
Now identify test cases which are affected by this changes and make clone test cases of them with changes.
Close your all old defects which are raised in this module and do not need now because of changes.
and execute all that test cases again and check system ans raise new defects.