Tip: avoid loops. The ChatService already has events that you can connect to for an event-driven system. If possible always try to enforce an event-driven system so your code is acting when these things are expected to happen. Loops should be used scarcely.
local ChatService = require(game:GetService("ServerScriptService"):WaitForChild("ChatServiceRunner").ChatService)
local function speakerAdded(speakerName)
local speaker = ChatService:GetSpeaker(speakerName)
-- Do your SetExtra data here
end
ChatService.SpeakerAdded:Connect(speakerAdded)
for _, speaker in ipairs(ChatService:GetSpeakerList()) do
speakerAdded(speaker)
end