Christopher, LG G3 Logic Board Motherboard Replacement service is not provided at ifixit, We can give info. on how you do it yourself or you can find a local computer/ cell phone repair shop to do the repair, make sure to get an estimate on repair.
How To Change is shown in the attached link.
Prices on replacement logic boards can vary a lot, you can go on line and compare prices, if ordering make sure to check the rating of seller to help avoid problems. Check the attached links,instruction and guides, Good luck.
I hope this helped you out, if so let me know by pressing the helpful button.
https://www.youtube.com/watch?v=ArBkw27uOJ8
http://www.ebay.com/bhp/lg-motherboard