Yes, you can update master labels of Custom Labels and translations using the "Quick Update Translations" app. Follow these steps:
- Open the "Quick Update Translations" app and navigate to the "Quick Update Translations" tab.
- From the "Select Entity to Translate" section, choose "Custom Labels".

- This will open the "Update Custom Labels Translations" page.
- In the "Select Custom Labels" section, pick the labels for which you want to update the master label and its translations.
- Under "Select Language", choose the languages for which you want to add or update translations. Then, click the "Fetch Custom Label Translations" button.

- The page will display a table with the selected labels and languages.

- To update the master values, make changes in the "Master Value" column. For translations, update the values in the respective language columns.
- After making the necessary changes, click the "Save Custom Label Translations" button.

- If the update is successful, you'll receive a success message on the screen, and you can also verify your translations by clicking on the links associated with the label names.


- By following these steps, you can easily update master labels and translations for your custom labels using the "Quick Update Translations" app.
P.S. Discover Quick Update Translations, the simple way to update Labels and Translations in just a few clicks. Find it on AppExchange: https://appexchange.salesforce.com/appxListingDetail?listingId=fa9afbfe-74ff-4027-ac32-2cdfd58184d3