This is the 92nd most frequent German word.
einmal
"Einmal" means "once" or "one time" in English.
In this sentence, 'einmal' softens the command and makes it more polite, essentially meaning 'just once' or 'for a moment'.
Komm bitte einmal hierher!
Come here once, please!
Here, 'einmal' refers to an instance in the past, implying 'once' or 'before'.
Ich habe das schon einmal gesehen.
I have seen this before.
In this usage, 'einmal' encourages attention or action, used to focus the listener.