A CanCollide Command?

First, use string.sub() to get the substring of the msg that the player has chatted using the player event.

Get the player by using PlayerAdded. You must do this in a regular script. You can use Local scripts for this but the local script would get copied and there would have to be 1 local script per player instead of just 1 script for the whole server.

game:GetService("PlayerAdded"):connect(function(player)
	print(player.Name) --Get the player's name.
end)

See if they have chatted using the chatted event.

game:GetService("PlayerAdded"):connect(function(player)
	player.Chatted:connect(function(chat)
		if string.sub(chat, 1,8) == "/unlock " and workspace:FindFirstChild(string.sub(chat,9)) then
			workspace:FindFirstChild(string.sub(chat,9)).CanCollide = false
		elseif string.sub(chat, 1,5) == "/lock " and workspace:FindFirstChild(string.sub(chat,6)) then
			workspace:FindFirstChild(string.sub(chat,6)).CanCollide = true
		end
	end)
end)

Or you can do this to just lock the spawn.

game:GetService("PlayerAdded"):connect(function(player)
	player.Chatted:connect(function(chat)
		if string.sub(chat, 1,12) == "/unlockspawn" then
			workspace.Spawn.CanCollide = false
		elseif string.sub(chat, 1,5) == "/lockspawn" then
			workspace.Spawn.CanCollide = true
		end
	end)
end)

If you want to do this in a script:

function lock(part)
	part.CanCollide = true
end

function unlock(part)
	part.CanCollide = false
end

lock(game.Workspace.Part)
unlock(game.Workspace.Part2)

Hope it helps!

If you only want some people to say it:

admin = {"LordDragonZord", "Player1"} --Add your name here. Add as much people as you'd like.

game:GetService("PlayerAdded"):connect(function(player)
	player.Chatted:connect(function(chat)
		for _,AdminName in pairs(admin) do
			if player.Name == AdminName then
				if string.sub(chat, 1,8) == "/unlock " and workspace:FindFirstChild(string.sub(chat,9)) then
					workspace:FindFirstChild(string.sub(chat,9)).CanCollide = false
				elseif string.sub(chat, 1,6) == "/lock " and workspace:FindFirstChild(string.sub(chat,7)) then
					workspace:FindFirstChild(string.sub(chat,6)).CanCollide = true
				end
			end
		end
	end)
end)

Or...

admin = {"LordDragonZord", "Player1"} --Add your name here. Add as much people as you'd like.

game:GetService("PlayerAdded"):connect(function(player)
	player.Chatted:connect(function(chat)
		for _,AdminName in pairs(admin) do
			if player.Name == AdminName then
				if string.sub(chat, 1,12) == "/unlockspawn" then
					workspace.Spawn.CanCollide = false
				elseif string.sub(chat, 1,5) == "/lockspawn" then
					workspace.Spawn.CanCollide = true
				end
			end
		end
	end)
end)