Here are a few guides and teardowns that may help you along with a few places to find the replacement part.
http://www.myfixguide.com/manual/lenovo-yoga-tablet-2-disassembly/
https://www.youtube.com/watch?v=KDr9BkeDwmU
https://www.amazon.com/90004973-Lenovo-Ideapad-VIUU3-Button/dp/B01NBN26KL/ref=sr_1_10?ie=UTF8&qid=1514229784&sr=8-10&keywords=lenovo+yoga+2+power+button
https://www.ebay.com/sch/i.html?_from=R40&_trksid=p2380057.m570.l1313.TR0.TRC0.H0.TRS0&_nkw=lenovo+yoga+2+power+button&_sacat=0