The first line you see says Documentation. Start by reading that.
The library covers many types of i2c displays, and you need to use the correct i/o class for the backpack displays using the i2c expander.
Examples->hd44780->ioClass->hd44780_I2Cexp
Then you want to run the sketch called "I2Cexpdiag " which is an i2c LCD i/o expander backpack diagnostic tool. Report the results of running that sketch.