If you knew a manager is 100 percent wrong about something, how would you handle it?

you need to give the recommendation to your manager that something is wrong & give him suggestion for solution how to correct it, by doing this you already contribute to solve the problem & your manager feel that you help him/her instead of only complain that he/she is wrong

Yo should be daring to let him know politely without hurting his ego.

1.You can constructively advice him on such issue.

2.You can be subjective backing your ideas with principle and theories

3.You can tell him that the disadvantage is more than the benefits

4.explain cost and effect of every action he carry out

Thank you for the invitation

I Agree with answer  Edwin 

Thanks 

I support Edwin's answer 

Regards 

Been there several times. Fact is it isn't your role to argue his/her position. It is their risk, their job to make these decisions.  

All I would really do is send an email (polite) - Noting that you will follow all instructions in relation to this specific decision - pointing out that you feel strongly that the decision is not the best way forward and the outcome  - and what you would recommend

Your question is not clear

If the manager  is per cent wrong about something

I must be either

A colleague

A subordinate

A collaborator

An auditor

An owner

OR A MANAGER OF ANOTHER STRUCTURE OR UNIT OR DIRECTION

There may be two managers of two different structures, units or directions

I try to point out to him indirectly and politely that he is wrong and I give him my opinion on the matter and I offer suggestions

The manager who is wrong, must opt for the style of participatory management