en_tn_condensed/act/12/06.md

On the night before Herod was going to bring him out for trial

That Herod planned to execute him can be clarified. Alternate translation: "The happened on the day before Herod was going to bring Peter out from prison to put him on trial and then to execute him" (See: rc://en/ta/man/jit/figs-explicit)

bound with two chains

"tied with two chains" or "fastened with two chains." Each chain would have been attached to one of the two guards who stayed beside Peter.

were keeping watch over the prison

"were guarding the prison doors"