Improving my antenna

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:

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.