https://youtu.be/UXVYq9pRXbc
You need to manually backup your savegame folder.
C:\Program Files (x86)\Steam\steamapps\common\GirlsCivilization\Gciv21V\Saved\SaveGames
Copy entire 'SaveGames' folder somewhere before update
because all save file will be removed while updating.
Update scadule is below
Pacific Time,
3 May 2019
10:00
China
4 May 2019
01:00
Washington DC
3 May 2019
13:00
日本時間
5月4日 02時
You don't have to do this again for further updates.
It was first time to me publishing in steam so I didn't know save files folder have to be generated only by user computer to prevent dumping save files while update.
Sorry for your inconvenience.