Question: There was accidental declaration of an informant of a death as the deceased. A family member of the informant is now worried that unfortunate things might happen. What can be done?
Answer: You should get the one who made the mistake to visit and apologise in person, explaining why it was ONLY a moment of unmindfulness that led to the administration error. Just as the one NOT declared deceased (who WAS really the deceased) did NOT come back to life just because of the error, the one accidentally declared deceased will NOT die due to the same error.
For more assurance, you can bring up examples of large-scale misreporting of celebrity deaths, what more with ill intent, with the misreported ones still living today: https://www.biography.com/people/groups/celebrity-death-hoaxes This is proof that such errors do not cause death.
The Buddha taught that death is eventual, and can arrive at any moment in time: https://thedailyenlightenment.com/2012/04/with-every-breath-you-take As such, there should not be fear of death, but calm and clear preparation for it, by studying and practising these teachings well: www.purelanders.com/now
This is how anxiety can be relieved with related Buddhist chanting practice: https://purelanders.com/2018/05/09/can-nianfo-relieve-anxiety These can be learnt systematically and comprehensively in courses at www.TheDailyEnlightenment.com/courses