Changing my gamer tag

Hey I was wondering if anyone can help. I was ranked 4th in halo reach living dead then I changed my name and now it says I’m 4,088. I know you can migrate stats because ive. done it before but forgot how. Can anyone help? It’s only been about 3 days since I changed my gamer tag. Thanks.

To sync up your stats you just need to play a few games of Reach on your new gamertag, after a short while everything should sync up again