If you wanna have a custom victory condition, then do this:
1: Go to scenario data
2: Enable custom victory condition
3: Choose one of the first traits possible to get in the "Game Win Trait" -Field

If you don't wanna have a custom victory condition, then do this (This one I learned from @indigofenix):
1: Go to the events tab
2: Make a new event
3: Put event counter treshold to zero
4: Make a global condition
5: Choose "Set Variable"
6: Choose Variable
7: Choose population - Infected percentage
8: Choose numerical value - 100
9: Make a outcome
10: Choose set variable
11: Time - Days until game win
12: Numerical value - 0

And there you have it. The second option needs Event lab to be enabled. Hope this helped.