LG Prime Plus screen problem

Hey guys what's up so I have this lg prime plus here with me and whenever I go and make calls the screen blacks out and doesn't turn back on no matter what I do. Even sometimes when not making calls it goes black and won't turn on completely. It turns on a bit but goes black again. This is a really serious problem as it doesn't let the owner use their phone and it wastes money through on-going calls no one can interact with. How do I fix this? Thanks for the attention

 

Bump please help

 

Where is that located? What can I do?

 

Thank you, but, isn't there a way to permanently solve this problem so the owner of the phone can use it normally?