How do I turn off autocomplete?

If you're referring to the autocomplete suggestions on koikoishi.eu.org when searching, you can turn this off by going to https://koikoishi.eu.org/settings and turning off "Autocomplete Suggestions”.

If you're referring to the suggestions when performing a search in the DuckDuckGo mobile app, you can turn this off by going to Settings > Private Search and then turning off "Autocomplete Suggestions" and/or "Recently Visited Sites".