I was already four weeks pregnant when I met keith in September. Keith knew I was pregnant and decided to continue to date me. After a few short month, keith and I got married January that same year. My daughter was born the following May, in Washington. Legally we had to put my husband as the father on the birth certificate, even though he is not the biological father. I want to change her last name to her biological fathers and also change her birth certificate to read her biological father as "father "
Where do I start?
How do I do this?

Keith, since he is the legal father will have to agree to this. In either case, you will need to file a petition in court for a change of paternity and amendment of the birth certificate.

You will need to have a paternity test done to confirm biological paternity.

Getting a lawyer to handle this would be a good idea.