What to do if a junior has a high-level checklist on the project?

Assign the junior to study the subject area and decompose the high-level checklist into more detailed test scenarios.

Discuss with him the areas of responsibility and the sequence of testing.

Control the decomposition process, check the completeness and adequacy of the created test cases.

Assist with mastering tools for working with checklists/test cases (e.g., TestRail, Zephyr, Allure TestOps).

Provide feedback and support during the testing process.

Encourage independent learning and question formulation.

Consider the possibility of pair testing to demonstrate best practices.