i just bought Hisense 43A7100F Smart 4K at 4 days ago, just reliased that with different viewing angle of TV, the TV brightness and colour will loss one. I ask the seller, he says cannot adjust. Is it true?

Can I know how to adjust TV best resolution?

I have new Hisense Smart 4K UHD (Hisense 43" 43A7100F Smart 4K UHD A7100F) , i am trying to adjust the TV brightness and contrast to find the best picture setting for personal viewing.

When i am trying to adjust to lower brightness, the TV image look dark.
When adjusted to more brightness, TV image look ok but when the screen with white colour object (example white background or a lady wearing white baju or a car with white colour), the screen look very bright.

Any good advise ?