Problem with Builder / Composer to edit pages elements – Only HTML avaible

Hello!

I would like to ask about how to edit pages becaouse template got no builder / composer.
When I try to edit pages, the only thing I see in page edition is html code and nothing more.

I would be grateful If you could tell me how to install builder to not delete pages and create them again from begging and insted of this just edit the pages you have created.