If you change your original content, the translation of this content remains unchanged.
For example, your Shopify store is translated into English and German. Let's imagine, that you have a text in the product's description "Hello world". It is translated into German "Hallo welt".
Now you want to change the English text or add some description like "Hello world, my friend". You change it in English, but in German it will stay "Hallo welt". If you want to change the content in German, you should translate in manually or automatically.
To translate it manually, please, follow the instruction from this article - Can I edit the translations manually?