Stay calm at all times. Be aware that one human error easily leads to another unintended human error.
If possible ask a colleague to relieve you of your tasks or ask your supervisor to get a replacement. Make a mental note of the situation or take notes. Note the time. Take an objective look and record for yourself WHAT happened and HOW. Try to talk to your colleagues about the safety event. What was involved? Avoid any signs of early judgment on good and bad actions. Try to describe as accurately as possible the circumstances of the event: people, systems, procedures, environment. Note any production pressure that could be present. Try to remember your actions and especially WHY you did those. These will be crucially important during later interviews.
Expect to be treated fairly and justly. You did not start out to deliberately make errors. The organisation wants to learn WHY it happened so they can prevent it from happening again; or prevent your colleague falling into the same systemic trap. No blaming and shaming should be involved.