Hello,
Shop page is a functional page and it should not be edited.
HTML block is added to the top filters. Please follow these steps:
1. Enable Top filters in the Theme Settings > Shop > Shop filters https://gyazo.com/3564df2a5d658a0010b6c0ebd0b537d4
2. Enable Shop filters area always opened
3. Shop filters content type should be set Custom content
4. You can choose the HTML block with the content from the Shop filters custom content drop-down.
Best Regards