If you've installed Cattr via Docker you can try to re-install it, or try to reset your password via password reset feature, or you can create a new admin in your instance via connecting to the Docker console.
If you'll choose the second option, run
docker exec -it cattr sh -c "php /app/backend/artisan cattr:make:admin YOUR_NAME YOUR_EMAIL YOUR_PASSWORD" at the server, where you has been installed Cattr via Docker.
Elsewhere if you installed Cattr from source you can run
php artisan cattr:make:admin YOUR_NAME YOUR_EMAIL YOUR_PASSWORD at the directory with the backend part.