Connect an external monitor to the laptop (TV- HDMI) and check if the display is OK.
If it is then there's a backlight problem with the laptop's display.
This could be due to a problem on the motherboard, a faulty video cable/cable connection between the motherboard and the display panel or perhaps it is a faulty LCD panel.
Please confirm the full model number of the laptop as it may be required to get the correct parts e.g. video cable or LCD panel or the schematics for the motherboard.
I think that your model is a Dell Inspiron 14 5491 2in1
If so then here's the service manual that will help you.
On p.35 it details the procedure to remove the display assembly.
This is useful in several ways as it will allow you to check the eDP cable (video cable) connection on the motherboard to make sure that it is secure.
It will also allow you to test for the backlight power on eDP connector pins 17, 18 & 19.
Here's an image showing where the backlight power comes from in a LA-711P motherboard. This hould be the motherboard number (printed on board) for a Dell 5491 2in1 laptop.
(click on image)
If the eDP cable connection seems secure and the backlight power is on the pins then it is in the cable or the LCD screen but looking at the service manual it appears that the display assembly is a complete module i.e. cable, LCD panel, lid cover etc. as it doesn't show how to disassemble it further.