Solved How Do I Return Solder The Tristar Logic Board Do I Need A Special Flux Iphone 6 Tristar Replace

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I took off TriStar iPhone 6 and I can’t seem to solder the tin Lin to the pin on the logic board of the TriStar do I need special flux and solder iron so do so . I see youtube do it but when I do it it won’t stick to the pin please help I am noob