This has already been covered here:
https://dietpi.com/forum/t/after-fresh-dietpi-install-ive-installed-some-software-and-reboot-now-ssh-says-warning-remote-host-identification/6265/1
ssh-keygen -R <YOUR HOSTNAME/IP>
This has already been covered here:
https://dietpi.com/forum/t/after-fresh-dietpi-install-ive-installed-some-software-and-reboot-now-ssh-says-warning-remote-host-identification/6265/1
ssh-keygen -R <YOUR HOSTNAME/IP>