How I can add data-toggle="modal" into existing menu item link?

Hi there,
I am a newbie, and I want do modal window using Bootstrap 3.
I need:
- add into existing Drupal menu item (in tag <a>) attribute data-toggle="modal",
- change link path to href="#myid" (but I have an error "The path '#myid' is either invalid or you do not have access to it.")
The problem seems easy, but I can not solve the problem.
How can I do it?
Thx for all answers.