Mass Update Account Data with Dataloader.io

To mass update your Account data (instead of mass deleting and reimporting) it is best to use reporting and dataloader.io from MuleSoft.
 

1. Create a report with the report type of Accounts.
2. Remove all of the fields in the columns and choose only Account ID, Account Name, and any other optional fields that might need to be mass updated.
3. Click on the filters tab, change the filter criteria to be all accounts.
4. Run the report and then export the report to a CSV file.
5. Make any and all updates in the CSV file for the data that needs to be mass updated.

From here, go to the website dataloader.io. If this tool has never been used before, be sure to click Login with Salesforce button and allow the dataloader.io and Salesforce instance to be linked together. After being successfully logged in, follow these steps:
 

1. Click New Task and then import.
2. The operation should have Update chosen.
3. Click Next and upload the CSV file.
4. Ensure that the Account Id is correctly mapped to the source header and then also ensure that any other relevant fields are also mapped. Please note that the field 'Account Name' is not necessary since data importing tools will use the ID rather than the name.
5. Make the Batch ID smaller. The smaller the batch size is, the less error-prone the data import will be. It will take longer so use your best judgement and then click Save and Run. 

Note: Dataloader.io from MuleSoft is a third-party data management tool that connects to Salesforce via API and can be used to mass update records.