Help with this sentence, please!

[serabourg]

当サイトの開設日4桁と沖田総司さんが亡くなった日付4桁（旧暦）を続けた8桁の数字です。
(The website's opening date is 2015.09.30 - the date Okita Souji died is July 19, 1868)

I'm supposed to decipher a password out of this sentence - but I'm not sure how to . . . follow the instructions (?). I might be making a fool out of myself, but I don't understand this. At all. Thank you to anybody who takes their time to go through this. I've been screaming internally from the frustration.

 

[Mike Cash]

Did you try 09300530?

新暦と旧暦の変換計算（長期）

You have to convert the death date back to the old lunar calendar.

 

[Kraise]

Did you try 09300530?

新暦と旧暦の変換計算（長期）

まさに暦交換計算サイトを調べようとしてたｗｗ

 

[serabourg]

まさに暦交換計算サイトを調べようとしてたｗｗ

今そうします！ありがとうございました~

 

[serabourg]

Did you try 09300530?

新暦と旧暦の変換計算（長期）

You have to convert the death date back to the old lunar calendar.

You're amazing. Thank you so much.