pls help me

If you want to emphasize that you want to see it with your own eyes you can said : 我要亲眼去看那达慕大会
If you want to emphasize that you want to go by yourself to see the conference then you can say: 我想亲自去看那达慕大会
But you can not say : 我想自己用眼睛去看那达慕大会。(chinese people dont say like this) 😀
I hope my explanation help.

Alternatively
我想亲自去看... to emphasize that you want to go there in person
Or
我想亲眼看... to emphasize that you want to see it with your own eyes *if you insist on using both 去 and 亲眼，you could say
我想去(place)亲眼看达慕大会。

我想亲眼去看那达慕大会。

我想亲眼看一次那达慕大会。
You don't need to add 去 because it is implied by you being there to see it.
I think adding 一次 makes the sentence sound more smooth.
You could also say
我像亲眼看看那达慕大会。

我想亲眼看看那达慕大会

我想亲自去看那达慕大会。

我想亲自去看那达慕大会。
亲自 is an adverb, which means [personally/in person/oneself].
For example,
这本书很重要，你一定要亲自给他。

我想亲眼看看那达慕大会。

我想亲眼去看那达慕大会

（改错句）我想亲眼去看那达慕大会。