Hello, there is more than 1 way of doing this.

One you add blocks to a page, you add them to areas. An area can be a global area in which case the blocks will be the same across all pages presenting that global area. To use that you'd have to be able to manipulate your theme's page types to add global areas.

Another way of doing it is to use a stack. You create a stack from your dashboard and add your block(s) to it. Then instead of adding the block to your page, you add the stack. After that, modifications to the stack and the blocks in the stack will be reflected everywhere the stack is used.

Thank you. Will try with global areas. Stack thing is not working for me. Probably I'm doing something wrong ;)