base = game.Workspace.SurvivorCount
missionstxt = script.Parent.missions
if base.S1.Value == true and base.S2.Value == true then
missionstxt.Text = "Mission One Complete!"
end
This script's location can be found here. This script is supposed to detect too see if both values are true, and if they are, they change the text of the textlabel (variable missionstxt).

3 comments
Thanks :D
Two changed events are not necessary, considering that you want BOTH values to be true. One or the other would be sufficient.
@Percil, what if S2 changed first and S1 second, then the Script wouldn't run.