Hello @PedroRodriguezxX, how do you want the default value to update? I am unable to assist without more information about exactly what you are wanting the desired result to look like.
How do you want the legend to be named on load? Is the default going to be different depending on the user that is viewing the dashboard?
What do you want to happen when one of the 2 dropdown controls is changed? Should the legend return the exact same name? What do the controls display on default when the user loads into the dashboard? What happens if both of the control dropdowns are changed by the user?
If you are able to provide more information about the functionality that you want in the dashboard, then @Brett and I should be able to guide you towards a solution. It would also be beneficial if you could create a demo version of the dashboard in Quick Sight Arena and share it with us. That would make it easier to test out possible solutions in an Analysis environment and share the results with you directly.
Thank you!