ohhh... It's very hard... in Hardware side.
First, Solder NEVER MELT.
Second, eMMC NEVER RIP OFF.
Last, Replacement eMMC NEVER STICK ON PAD.
well, so I break my PW2 lol. try again to get another Mainboard.
PS. I've found author's detail guide here. (Chinese)
(1),
(2)