Hi Victoria,
Unfortunately, your requirement is not feasible via Power Automate > Update a Row. The Key value should be associate with a unique value in your Excel worksheet. If you have duplicate values, as a result, it will only update the first row which has the key value match.
For your requirement, you will need to use the Office script as described in the following thread:
how to update multiple rows with a key value
Meanwhile, as the Power Automate related questions are not fully supported in this community. To make sure you get the best answers to your concern, please post a new thread in thePower Automate Community.
Appreciate for your understanding.
Regards,
Alex Chen