He could just stop fighting the extradition unless there are concerns he wouldn’t get a fair trial in the US. I haven’t heard of such concerns and he could probably get a solid legal defense team with private donations.
I have no particular viewpoint regarding Assange, but depending on your understanding of "fair", there are probably many whose fairness can be questioned. Partiality of judges, imbalance of legal team budgets, etc. Look at any case brought up by a patent troll against a small/medium business.
One case that personally always bothers me was regarding the murder of Philando Castile.