Guardians cannot reset family member password

a member of our family sharing has forgotten their password, and neither guardians nor organiser can reset it.

We both get a message on our phones saying “Because this is a new device you cannot edit account information” and then lists the family member’s device to use.

they’re can’t be used as they are a child and the settings stop them being able to amend their own password.

Neither of our devices is new, and both have been used to set up or change settings in the family group before.

Any suggestions?