To change the SEO title and description for your bundle landing pages, you can simply open your theme's layout/theme.liquid file and adjust the code in the header section.

You can use these variables values for meta tags on landing pages: 
{{ bundler_bundle_title }} <- Contains bundle title (only available on landing pages) 
{{ bundler_bundle_name }} <- Contains bundle name (only available on landing pages) 
{{ bundler_bundle_description }} <- Contains bundle description (only available on landing pages) 
{{ bundler_bundle_image }} <- Contains custom bundle image (URL) if the bundle product level is set to variant level and the image is set (only available on landing pages) 

{{ bundler_page_type }} <- Let's you know if we are on a bundle landing page or bundles listing page. 
When on the landing page, the value will be 'landing-page', when on bundles listing page, the value will be 'listing' 

Here is an example how you can use these variables to set a SEO page title for your bundle landing pages and bundles listing page. 
{% if bundler_page_type and bundler_page_type == 'landing-page' %} <title>{{ bundler_bundle_title }}</title> {% elsif bundler_page_type and bundler_page_type == 'listing' %} <title>All bundle offers</title> {% else %} <title>{{ shop.name }}</title> {% endif %}The first statement takes care of the bundle landing page, where the title gets set to the title of the bundle. 
The second statement sets a title for the bundles listing page. 
And the third statement sets the shop name as a default title in your shop.