These are the save file locations by platform:
Ubisoft Connect
C:\Program Files (x86)\Ubisoft\Ubisoft Game Launcher\savegame\<UbisoftConnectID>\5059
Steam
C:\Program Files (x86)\Ubisoft\Ubisoft Game Launcher\savegame\<UbisoftConnectID>\5092
Playstation 4
Settings > Application Saved Data Management > Saved Data in System Storage > Assassin's Creed: Odyssey
Xbox One
My Games and Apps > Assassin's Creed: Odyssey > Menu > Manage Game > Saved Data
In some cases, we may ask you to provide your save files.
For more information on which save files to submit to us, please check our dedicated article.