Hello,
Thank you to all for responses. Big problem seems to be Thailand not a part of 1961 Hague Apostille treaty. So it look like I need document authenticated by home government, then Thai Embassy at home, like you did. Problem is, we are here now, not there! Thailand such mess sometimes. I think maybe I Thai Embassy can authenticate and then I can bring to Thai MFA confirm. Then after all that, maybe can use at immigration to change visa type.