Have an HTML file saved somewhere to use for the procedure.
Right click on it, and select 'Open With' and go to 'Choose Default Program'. In the window that pops up, if Notebook is present select it; if not, click the 'Other Programs' dropdown, and look for it there, or failing that, browse to Notepad.exe
Lastly, select the program with a single click, not a double click, and untick the box below the browse window 'Always use the selected program to open this kind of file'.
After doing that once, Notepad should be added to the list of programs, when you right click and 'Open With'.
Or...you can right click the HTML file, and go to 'Edit' if available, but you'll have to setup Notepad as the default HTML editor (it might be Wordpad).