Hi,
PIH will gradually resolve on its own even without any treatment. So waiting for spontaneous resolution is an option to consider.
If using a lightening cream to hasten resolution of PIH in acne-prone skin, choose a product with proven skin lightening ingredients (discussed in detail in other parts of this forum), avoid greasy composition and avoid steroids in the cream which may potentially aggravate acne.
Tretinoin cream may be a good first line option as not only does it possess lightening properties, it also possesses anti-acne properties.
Hope this helps!