Does that mean that you followed my instructions on how to install the library through library manager?
To install the hd44780 library. The hd44780 library is the best available for I2C LCDs. The library is available in the Library Manager. Go to Library Manager (in the IDE menus, Sketch, Include Libraries, Manage Libraries) and in the Topics dropdown choose Display and in the Filter your search box enter hd44780. Select and install the hd44780 library by Bill Perry.
If not, you need to install the library properly.
I tested the code before I posted it so I know that the code works.