German phrase
Sagen Sie mir bitte, wenn es ~.
Meaning
Please let me know if there is ___
When to use it
Ask to be told if it happens. Use this to request notice about a possible issue.
Example dialogue
Sagen Sie mir bitte, wenn es ein Problem gibt.
Please let me know if there is a problem.
Natürlich, ich informiere Sie sofort.
Of course, I will let you know immediately.