Search on Google for DOWNLOAD GARUDA INDONESIA and will go to this page below
Scroll down to #13 and download the Tier Matching Order Form from Garuda Indonesia site
Fill out form completely and take a picture of it. Also took a picture of my Singapore Airlines Star Alliance Gold physical card
and a picture of my passport for proof it is me
Screen shot of my Garuda Miles Blue membership card on the app
Sent all these in by email to email@example.com
One day later was informed by email: Hereby we inform you that we have received your documents and we will process your Tier Matching request. We will inform you again once the process is done.
The very next day the match was completed and my Blue tier was upgraded to Garuda Miles Platinum which is SkyTeam Elite Plus. Expires end of March 2020.
Skyteam Elite Plus gives you all the benefits below
Guaranteed reservations on sold-out flights
Priority at transfer desks
Priority at immigration and security lanes
Extra baggage allowance
Priority baggage handling
Priority baggage drop-off
Priority airport standby