iphone 7 plus no wifi connection and discovered burned board.

i recently purchased an iphone second hand that appeared to be in excellent shape. upon setup of the phone when asked for an internet connection the phone did not see any. got out my old iphone 6s and when it turned it back on it found my wifi instantly when the springboard came up. not a wifi access point problem. so i moved the 7 plus so that it was literally sitting on my router and it seen the wifi, it had problems connecting to the AP but managed to connect. i noticed there was signal strength fluctuations on the phone so i logged into my router thats running DD-WRT to check signal strength from that end and i could see severe fluctuations from there as well. so i got curious and searched for similar problems with the phone online and it lead me to the wifi diversity antenna thats attached to the loud speaker at the bottom. upon its inspection it appeared damaged like it had been shorted out. i bought another replacement diversity antenna and installed it with no change in how the phones wifi worked. i decided to fire up a 5G wifi access point and see if the phone could see that and yes it does see and connect to 5G wifi no problem. so that narrowed the issue down to the 2.4G antenna or radio in the phone. so back to research online. i come to discover that there is a wifi antenna in the upper left hand corner of the phone as well so i tore the phone back down to have a look a that antenna. when i got the plastic cover off of it i discovered that something had burned under it! not sure if something failed on the board or if that plastic cover that is supposedly the antenna itself had shored out somehow. what i want to know is if this is common problem with wifi shorting out and causing physical hardware damage and if i can replace the plastic part if that is infact the antenna and it will work again as normal. if this thing needs a new main board i basically bought a severely over priced ipod which sucks. pictures of the burned board are attached and a stock photo that i found online that i circled and pointed to the troubled area on the board.