How to remove stains from white clothing?

I'm hoping to find some information regarding removal of stains. I have many white clothes with some stains, especially under arm pit stains and have tried napi san, bleach ect but can't get them out and looking for someone to do some research into it and suggest to me how I can get my whites white... show more I'm hoping to find some information regarding removal of stains. I have many white clothes with some stains, especially under arm pit stains and have tried napi san, bleach ect but can't get them out and looking for someone to do some research into it and suggest to me how I can get my whites white again.
The fabrics are just cotton or cotton / poly
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