My recommendation is to ignore GolamMostafa.
Particularly post #7.
Things like "try this", "try that", are typically not helpful and just waste time.
What you want is advice that points you to something that really works.
In order to do that you need to be working with known s/w so you want to be downloading s/w from the REAL source not just some "random" site that has who knows what s/w and version or even a copy of somebody else's s/w.
This is why I can't say with strong enough words to avoid his #1 recommendation in post #7.
That is recommending getting and archived version of my hd44780 library, not only are you not assured that is an official copy but downloading and installing it from a site like that is more effort and prone to error and incorrect installation than installing it directly from the Arduino IDE using the built in IDE library cloud service.
As Don said there are many many threads about i2c backpacks on LCDs. There are many libraries called "LiquidCrystal_I2C" or that have a i/o class called "LiquidCrystal_I2C" and they do not all work the same.
Searching on the Arduino formum site is painful because the admins for the arduino site removed the forum search capability.
I've never worked on any other forum site (and I use hundreds of forums) that had no search capabilities.
Yes there is "search" on the Arduino forum but it isn't a forum search. It calls google to search the forum site.
While you can find information, it isn't nearly as useful as a true search capability that is built in to the forum s/w as you can't do simple things like search a particular sub forum or search for threads or subjects by a particular forum member.
Because of all this "LiquidCrystal_I2C" library mess, I created the hd44780 library package which can offer "plug and play" for i2c based lcd backpacks.
So My recommendation is to use a library that works, and that will be my hd44780 library.
It is available in the IDE library manager so you can quickly and easily install it with just a few clicks in the IDE.
You will need to read the Documentation as it describes where to find the examples.
The i/o class for an i2c backpack is hd44780_I2Cexp
The library also includes a diagnostic sketch, I2CexpDiag to test your i2c signals and LCD device.
Here is a link to the github page which has additional information including installation instructions:
With my hd44780 library package you can be up and running in literally just a couple of minutes after you spend a couple of minutes reading the documentation on the library that describes where to find the example for your i/o class.
Just remember, reading will be required so don't try to skip that part.