Picking up as chazan

Hi,

One who comes into the synagogue while the community is reciting the silent amidah should not serve as the chazan to repeat the amidah aloud unless he first recites the silent amidah as well. However, this rule may be waived where no one else can serve as the chazan.

(Rivivot Ephraim 1:86)

Have a great day,
Mordechai