wifi and bluethooth problem

my phone got submerged in seawater, and when i had the time to quickly disassembled it, there's a residue of the sewater, and tried to remove the residue of salt to prevent corrosion, after a few days, i managed to but thermal paste, kapton and copper tape and and b-7000, i used an electronic grade 99% isoprophyl alcohol to submerge the motherboard and clean the top part since it has the makrs of saltwater residue and brushed it gently, and clean the middle frame (top part) where a few residue of seawater can be seen, after reassembling the phone, i managed to power up the phone, all works, aside from the bluetooth and wi-fi connection, at the wifi, only a few times, it can detect the wifi but only at 1 signal and 2.4ghz only, it cannot detect the 5ghz and im not event 5meters away from the router,then disaapear right away, i assume the issue/problem has to do with the hardware, which part should i pay special attention to trigger the signal receiver or which part should i replace, is it the plastic back cover?, the middle frame ?

EDIT* i've added the close up image of the said antennas