This manual describes how to manually trigger an update on the product feed (data source) in Google Merchant Center Next
Click on the [1a] Gear-icon and then select [1b] Data sources.
Find the feed you are looking for look at countries and language columns. Then click on [2] Update.
Google will start downloading the feed which can take up a few minutes or more depending on the number of products you have. You should see the product data changes within 15 minutes after the feed is finished.