How can I make a script make a message that says "Team eliminated"?

You should probably take a look at Doomspire Brickbattle's scripts. This is what I found. The game link is https://www.roblox.com/games/5964395953

local c=y[s]:WaitForChild("GameValues",1):WaitForChild("Teams",1):GetChildren() -- values are being created inscript, using WaitForChild to avoid syntax errors 
					for g=1,#c do -- Begin scanning in order to associate the GameValues with the actual game
						
						if SpawnPart:IsA("SpawnLocation") then
							if c[g].Value==SpawnPart.TeamColor then -- If one of the BrickColorValues in GameValues.Teams is equal to the SpawnLocation's TeamColor (NOT the spawn's BrickColor), then ...
								
								c[g]:WaitForChild("Spawns",1).Value=c[g]:WaitForChild("Spawns",1).Value-1 -- ... subtract that team's spawn value in GameValues.Teams.[TeamName]. Remember, this is if one of the spawns is deleted.
								
								if c[g]:WaitForChild("Spawns",1).Value==0 then -- If you have no spawns left, then you lose.
									
									y[s]:WaitForChild("GameValues",1):WaitForChild("TeamsLeft",1).Value=y[s]:WaitForChild("GameValues",1):WaitForChild("TeamsLeft",1).Value-1 -- This is vital to the game ending as a whole.
									
									game.Teams:FindFirstChild(c[g].Name).AutoAssignable=false
									local msg=Instance.new("Message")
									msg.Text=c[g].Name.." TEAM has been eliminated!"
									msg.Parent=workspace
								end
							end
						end