https://www.gardeningchannel.com/how-to-fight-fusarium-wilt/

Solarization and Actinovate are two recommendations given, plus some other ones that don't seem all that realistic to me. :-)

Good luck, fusarium wilt's a toughie.

One suggestion I did find that seems sensible is to simply not grow things susceptible to it (I know, I know) for three to five years to give it time to fade. It may not completely take care of the problem, but should help.