Honestly your best bet would probably be to ask your close family and friends to look over you and give their opinions. The chances of finding someone who could do it who actually knows how to proofread and edit as skills to do it for free is almost impossible. And the skill level of random people online is most likely not going to be much higher than that of people you already know. So it would probably just be easier to ask for a favor from people you already know in real life. Easier to trust them than Randoms anyway.