You are using an old library and have an example that is incorrectly using the library.
I recommend using this instead:
You can google around for many of my posts about this.
Read both the github readme page and the wiki for
features & instructions on how to install it, (use the IDE library manager).
The i/o class you will use is hd44780_I2Cexp.
The library will auto self configure everything for you, including i2c address and pin mappings.
Run the included I2CexpDiag to test that everything is working.
See the hd44780_I2Cexp i/o class HelloWorld for a simple example of how to declare your lcd object and initalize the library/device.
--- bill