。
Fill it up, please.
Literal
Full-tank [with-で] please-[お願いします].
The pattern [noun]でお願いします is a polite-request shortcut common in service interactions — restaurants, gas stations, shops. The で marks the means or state ('with [full tank]'), and お願いします attaches directly to nouns without needing an intervening verb. お願いします is extraordinarily versatile in Japanese service contexts.