Dress White

How to get rid of stains from a white dress that says do not bleach?
A friend of mine gave me her white United Colors of Benetton white dress/nightie.
I found some minor stains that i want to get out, but it says “do not bleach”
On the tag its 100% polyester, if i bleach it, will something happen?
If it does, what can i do to get rid of these stains?
Soak it in a bowl of warm water and 1 scoop of OXY clean for about an hour. Then rinse the dress and make a new bowl of water and OXY clean. Leave it over night then rinse. I have gotten stains out of doll clothes this way and the stains had been in about 40 years.
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