Are you playing on android? If so, don't uninstall the old version. Just install new releases over the existing one.
Can you check here for your old save files?
Windows: C:\users\(username)\AppData\Local\UserData\Default\Lust Doll Plus
Mac: \Users\(username)\Library\Application Support\Default\Lust Doll Plus
Linux: \Users\(username)\.config\KADOKAWA\RPGMV\Default\Lust Doll Plus
(May need to sudo nautilus if you don't have access to .config)