Ash here from the Shopify team. Thank you for posting your question on how to change the wording in your checkout/thank you page.
If you've already checked in the Theme Customizer and the code of your theme, then the wording you're looking to change will likely be found in the Language Editor for your theme. Our Help Center has a section with information on how to change the wording in themes, but I'll also include some steps below:
Let me know if you're able to track down the wording you intend to edit. I'll be happy to further assist and help take a closer look if there's any trouble locating that.
Thank you for answering.
I'm sorry I didn't have enough explanation.
It's not the wording that currently exists. The real intention is to add the new wording to the specified location.
* This is a Japanese page.
I'm developing a Shopify app.
However, I don't think this method can be achieved when installing the app.
Please let me know if there is a method other than the above.
I'm sorry for my poor English.