While the majority of changes to your bundle settings and bundle page must be made through the app, your search engine listing preview can actually be edited through your dummy product page.
To find your search engine settings within your dummy product page:
Go to your Shopify admin dashboard, and select Products > All products.
Select the dummy product for your bundle.
Scroll down to Search engine listing preview, and select Edit website SEO.
You can use up to 70 characters to write the Page title, which will appear in search engine listings.
Using up to 320 characters, the Description is where you can input text and SEO keywords to improve the visibility of your product in search engine listings. This will not affect the description on your bundle page, as those changes must be made through the app.