Create a UML Comment containing whatever text you like.
Anchoring
You may wish to anchor your comment to any element in your model, but that is completely up to you. The rest of instructions apply regardless of anchoring.
Double-click the Comment to open its specification window.
In the specification window, click the three dots at the end of the Applied Stereotype field. A shortcut menu appears.
Start typing Annotation to search for the annotation stereotypes. You will see three stereotypes appear: Annotation, Literal Annotation, and IRI Annotation.