how do i improve my game graphics?

This is a very broad question, outside the scope of this forum. There are many things contributing to the final look and feel of the game: art direction, models, textures, lighting, level design, post processing, special effects. Those aspects are pretty much their own professions. If you are a loner developer then just jump in and learn whatever field you are interested in, there a lot of tutorials available on the internet. Get your feet wet with every stage of the development process so you find out which bits you enjoy the most and focus on those going forward.
And don’t forget that you can buy models, textures, Unreal ready asset packs from the Unreal Marketplace, CG Trader, Gumroad (just to name a few) so you have a rolling start.

I dont mean the editors graphics i mean the game itself, is it the material or am i just doing something wrong because when i see other indie games made by 1 or 2 developers it looks like a AAA game with its amazing graphics.
if its the material problem then thats easy to fix and focus on learning but if it isnt then what is?