Hi achraf lamhamdi
Here's the hardware maintenance manual for the laptop.
Go to p.93 in the manual to see how to remove/replace the LCD panel. If the LCD panel is faulty it can't be fixed, it needs to be replaced.
This will also allow you to check that the video cable connection to the motherboard is secure etc, in case that is the problem.
If you determine that the panel is the problem, here's a link to find the correct replacement part.
Type Thinkpad T470 in the search box and then select your exact model variant (look on product info label on bottom of laptop to find model type). When you're on the parts page, click on Select Commodity > LCD panels to find the part number(s) for all compatible panels. Then search online using the part number only to find suppliers that suit you best. Usually the part number can also be found somewhere on the back of the panel if you wish to verify and get the same one.