Hi Milind,
You may want to use "Import User Group Mapping" data import task. It reads the data from the following files:
- UserParentGroup.csv
- GroupSharedUserMap.csv
If you run the Import User Group Mapping task using the Update Only import operation, all existing group/user mappings for the groups in the UserParentGroup.csv file are replaced by the mappings in the GroupSharedUserMap.csv file