Explanation: It means that you don't have a "TextMeshPro" component on your GameObject.
Solution: Add a component that inherits from TMP_Text and then try again (you can add both the GUI or the 3DMesh one).
Please install the package "TextMeshPro", available in the Unity's package manager.
If you have errors after updating, please be sure to read the Updating Guide in the documentation.
If you're using Unity 2019.x or above and the Editor is not loading global effects, be sure that you have "ProjectSettings/Editor/EnterPlayModeSettings → Reload Domain" set to true and enter playmode once.
Please, be sure to read its related guide in the documentation and follow each step.
If it still doesn't work, feel free to contact me.
Explanation: "TextAnimator" is inside the "Febucci.UI" namespace.
Solution: Be sure to include "using Febucci.UI;" at the top of your script.