"Passers-by" is already plural.
The plural form of "passerby" is "passersby."
The singular form is passerby; the plural for is passersby.
The possessive form for the plural noun passersby is passersby's.Example: The passersby's attention is not drawn by our display.
The plural form for the compound noun passer-by is passers-by.
passersby
The noun 'passerby' is the singular form. The plural form is passersby.
passersby
Passerby
There is no plural form. Do and Do not are verbs
The plural form of him, her, or it is them. (objective pronouns)
Bridges is the plural form of bridge.
The plural form of "was" is "were."