There's a really helpful step-by-step guide on fitting thread inserts in this month's Practical Sportsbikes magazine. I've sent you the relevant pages via PM. You can ignore the first six steps as the hole has already been tapped for you, although it might be a good idea to run the tap down the hole to ensure the thread is clear.
You'll need a replacement insert and insertion tool. Machine Mart do an M6 kit for £16.79,
https://www.machinemart.co.uk/p/040216677/ which should do the job.
Hope that helps.