flour/ roux, you put flour in bowl you add the hot broth from you soup , however a teaspoon at time, wisking and stiring much, you do you add to the soup, you do in batches until reach consisteny its called a slurry.
you can also use, breadcrumbs plain or mash cooked rice or pototao again , in bowl add broth from soup stiring , add into soup pot, repeat until consistency you wish