“Someone else should learn this” often remains on a manager’s list until the person who knows the task is unavailable. A smaller starting point is more workable: identify one important task that a second person could perform safely with the right support.
Choose a task with a clear beginning and end. “Understand the entire department” is not a training objective. “Prepare the weekly stock exception summary and send it to the reviewer” is specific enough to observe and practise.
Capture the decisions as well as the clicks
Ask the current task owner to explain the inputs, the expected output, the checks they make and the point at which they stop and ask for help. Screenshots can show a button, but they rarely explain why an unusual entry should not be processed.
Document access requirements through the normal permission process. Cross-training is not a reason to share passwords or give a learner authority to approve their own work. Keep review and approval boundaries intact.
Let the learner do a complete rehearsal
Begin with a demonstration, then let the learner work through a safe example while the experienced colleague observes. The learner should use the draft instructions rather than relying on continuous prompts. Every place they hesitate is useful feedback about the documentation.
Include one ordinary exception, such as a missing input, without turning the session into a surprise test. Ask the learner to show where they would seek help. Successful training includes recognising when the routine no longer applies.
Agree who maintains the instructions, how often the backup person practises and what happens when the underlying process changes. Also make time for the person providing the training; treating documentation as invisible extra work can undermine the project.
After the rehearsal, record the remaining limits honestly. “Can prepare the summary with review” is more useful than “fully trained” when approval or unusual cases still require another colleague. Expand to the next task only when this first one works in practice.