Hi, im using netgear wndap360 with openwrt 19.07. How Can i set antenna of 2.4GHz wi fi to internal or external? Now I don't even know which I'm using 
You're using all antennas on the band - you can't pick.
It seems like you're describing settings on old 802.11b devices and not newer WiFi technologies.
Basically all devices hardwire the radios and antennas.
This access point has possobility to use external antenna instead of built-in. This option was possible to choose from original software because external antena is not required. In original software description was something like you Can use only internal or external antenna not both in the same time