Hi @Naveen10 ,

I do not quite understand your requirement. If in incident is assigned to an assignment group, and the assignment group changes, you want to cancel the SLA and create a new SLA whit retroactive start? is that correct understood? If yes, why cancel the first SLA? What will you benefit from cancel the first SLA? 

if my answer has helped with your question, please mark my answer as accepted solution and give a thumb up.

Best regards

Anders