Can I open the door manually?
'Manualmente' — ma-nu-al-MEN-te. Five syllables; stress on the fourth.
Ask or say this if you are on an older metro train where doors must be opened by pressing a button or pulling a handle. On newer automated trains, doors open automatically.
'Manualmente' is an adverb formed from 'manuale' (manual) + '-mente' (the Italian adverb suffix equivalent to -ly). Italian forms most adverbs this way: 'lento → lentamente', 'rapido → rapidamente'. 'Aprire' is an irregular -ire verb (first group: apro, apri, apre…).
Come si apre questa porta?
How do you open this door?
More practical question when you cannot find the mechanism.
C'è un pulsante per aprire?
Is there a button to open it?
Asks specifically about a button.
La porta si apre da sola?
Does the door open by itself?
Check if it's automatic before touching anything.
Older rolling stock on Rome's metro line B and Milan's older lines requires passengers to press a green button to open the door. On newer automated lines like Rome's line C and Milan's M5, doors open and close automatically with no buttons needed.