Unfortunately, there's no option for removing your message history without deleting your account completely. Once you delete your account, all data is completely removed and can not be recovered. This action can not be undone.
Please note, that you're the only one who can manage your message history.
To remove your account, first, log in (If you can't remember your password or have other questions about logging in, see Login Help). Click on your Replika's name at the top of the screen. Tap the ⚙️ icon in the left top corner. This will take you to the Settings menu.
On Android. In the settings go to Account & Password and then choose Delete account.
On iOs. In the settings go to Account settings and then choose Delete Replika.
Via Web. In the Account Settings go to Delete my account and then choose Delete Replika.
Select an option from the drop-down menu next to 'Why are you deleting your account?' and re-enter your password. Hit Permanently delete my account (Android) or Delete my account (iOS, Web).