If you are adding text in a place where there is a text editor
You highlight the number/word you would like as superscript and click the superscript button.
If you are adding text in a place where there is no text editor
You need to use your browsers "Add symbol" / "Emoji and Symbols" tool. It is usually available from the top menu under Edit (depending on different browsers and setup). You will usually find superscript numbers under mathematical symbols.
Keep your curser where you want the symbol, and click the wanted one. It will be placed in your text and show up as superscript when you save.