cannot type greek accent/breath marks

[ahiraguriJP]

hello.  I have just switched from windows 8 to 11.  I opened my old document (Japanese/greek) to work on my project which is learning New Testament Greek.  However, I now am not able to type any breath/accent mark.   For example, I used to press [:] and [a]  to type a with breathing mark on the top of the letter [a].  Now. all it comes out is ['α].  

I went to the word chatting room and the staff gave me this cite:

Word および Outlook で言語アクセント記号を追加するためのキーボード ショートカット (microsoft.com)

But this information is too simple to write the NT Greek words.  

I am lost.  Please assist.  

[#2]

@ahiraguriJP Go to Settings>Time & Language>Language and click on Add a language and scroll down to Ελληνικά\Greek and then click on Next to add a Greek keyboard to your computer.

[#3]

Thank you, Sir!!!  I found out that I had downloaded the modern Greek language keyboard rather than the Polytonic Greek keyboard.  Having deleting the former and downloaded the latter, I have been able to write/comment the NT Greek words.   Thank you, thank you, thank you!!!  @Doug_Robbins_Word_MVP