1. Go to the local household registration police station or file storage unit, submit grandparents' ID cards, household registration books and other relevant documents, and apply for correcting grandma's name in grandpa's file.
2. According to the relevant procedures, it may be necessary to provide some supporting materials, such as family members' relationship certificates and death certificates, to prove that grandma's name should be corrected.
3. After submitting the application, wait for the household registration police station or the file storage unit to handle it. Processing time may vary from region to region and usually takes some time.
It should be noted that the specific processing procedures in different regions and different units may be slightly different. Specifically, you can consult the staff of the local household registration police station or the file storage unit and go through the formalities.