Final answer:
The nurse should instruct the client to report black, tarry stool to the provider as it can indicate gastrointestinal bleeding.
Step-by-step explanation:
The nurse should instruct the client to report black, tarry stool to the provider. Black, tarry stool can indicate gastrointestinal bleeding, which is a serious concern and should be immediately reported to the healthcare provider. This finding can be a sign of underlying issues such as ulcers, diverticulitis, or gastrointestinal bleeding.