If you don’t know, it’s very likely best to just build one of the DIY self antennas (Three Easy DIY Antennas for Beginners)
Or just buy an antenna:
https://www.ebay.de/itm/Antenna-ads-b-collinear-1090mhz-white-great-gain-COL1090-5-H-Vinnant/303279152783
Or the FA antenna.
Or check here for a cheap ebay PCB antenna: Useful items for purchase · wiedehopf/adsb-wiki Wiki · GitHub
It’s tuned for GSM band, so what are you gonna do?
If you wanted to modify it, you would need an antenna analyzer.