How do I add an anchor attribute to a route?
Thanks everyone! 

I have solution my for problem.
You just had to add it to this my_module.links.contextual.yml file.

regions.taxonomy_term.edit_form_header:
  title: Edit this block
  group: region_taxonomy_term
  route_name: regions.taxonomy_term.edit_form_header
  weight: 10
  options:
    fragment: 'edit-group-header'