When you request a callback from the ISO team, the team will review the information you have submitted and do some background research to build up a picture of the case.
A member of the team will then call you at the agreed time to talk through the case, it may be that this will be something that will only require the one call or it may be that this will identify a longer piece of work.
Sometimes it may require further follow up work either via email/teams or through a face to face visit. This will be discussed when the ISO team make contact.