How to reset a registrant’s password ?
Hi, what do you mean? A registrant doesn’t have a password… but if it’s for an Indico account then users can reset it themselves using the “forgot password” option during login. There’s no option for an admin to force this for a user.
A registrant notife me :
“When I enter my email in the account creation field, the server replies that my email is already taken. Not having my password, I am blocked. I’m sorry but since I don’t see a link to reset the password, I can’t register.”
I don’t know how to help him.
Thank you 
Does your event require an Indico account to register? I’d suggest asking the user for a screenshot to know whether he’s trying to register for the event or to create an indico account.
In any case, the reset password option is on the /login page right below the form: 
Oh, you have LDAP/AD to login. Seems like the user does not have some mandatory data (but a valid password) in AD so the login fails with this error…
If they have a regular indico account they have to choose “Indico” as the authentication provider on the login page; then the reset password option will show up:
Hello,
Is it possible to recreate an account with the same email address?
Thank you