A Record-Triggered flow on the parent object will be necessary for this, with a simple Update Records element for the child record(s).
The below will explain how to do so from an Opportunity record. When its stage changes to Closed-Lost, all its related Tasks should update to Completed. You can apply the same logic to any parent or child object:
Step 1. Navigate to Setup
Step 2. In the Quick Find box, enter and click on Flows
Step 3. Click on the New Flow button and select Record-Triggered Flow and Create
Step 4. Add a new element and choose Update Records
Step 5. Click on the Save button and give your Flow a Name
Step 6. Activate your flow.
Note:
Please bear in mind that this will only work for newly created or updated Opportunity records. For existing ones, you'll need to manually update the Task status fields (maybe with the data loader) or create a scheduled flow that would run once on the Opportunity object with the same elements as the record-triggered flow above.
However, if you decide on the scheduled flow option, please remember that the combination of all scheduled flow filters in your organization can’t result in more than a total of 250000 records within 24 hours at the time of writing.
Therefore, if you have too many opportunities to update in one go, consider adding filters to the start element and running scheduled flows over a few days in order to go through all your existing opportunity records.
When an Opportunity closes as Lost, you may want to automatically complete all related Tasks
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Eric is a Senior Consultant at Epam PolSource and has been working in the Salesforce ecosystem for the past 12 years. He started his Salesforce career as a Salesforce support agent. Like many others, he stumbled across the platform accidentally and hasn’t looked back since. Eric is very active in the Answers community and has been a Salesforce MVP since March 2021.
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