Help me!

The usual form is "OK with me." Occasionally, and very casually, you will hear "OK by me" -- this is idiomatic, and can't be interpreted by simply translating the words. It means the same as "OK with me".

Another form is "OK to me" which would be used in a sentence like, "It looks OK to me," signifying visual approval.

I have not heard "OK for me" used, but it might be correct in some circumstances.

Thank you for being careful to use spaces after your punctuation. This is an important part of English style and it's good to see you have learned it.