It is recommended that you should update the Product Titles on Shopify, sync those updated titles inside the app and re-publish the product to update the same on Etsy as the application considers Shopify as the centre of all management.
However, if you intend to keep different titles on both the platforms, you need to disable the Auto Sync settings for "Title" in the 'Product Management tab of the Settings section. Refer to the below screenshot for disabling the Auto Sync settings for Title:
The application will not sync the Title field from your Shopify once this setting is disabled! After this setting is disabled, Update the Product Titles inside the app and re-publish the products to update the new Titles on Etsy via the app.
NOTE : Updating product titles directly on Etsy may result in data being overwritten which is present in the app. Therefore, recommended, you must update the titles in the app after disabling the auto sync settings.