”How do I transfer my Immigrant Visa case from one embassy or consulate to another?
If you would like to transfer your Immigrant Visa (IV) case to another embassy or consulate, please follow the steps below:
-If your case is at a U.S. embassy or consulate, contact the potential gaining U.S. embassy or consulate in writing to request a transfer of your case. Please include a justification for the request. If you are not a resident of that country, specify that in your request.
-If your petition is being processed at the National Visa Center (NVC), contact the NVC to request the transfer. NVC will transfer cases to another IV processing post if parties provide a written request along with the address in the requested country and the proof of eligibility (citizenship/legal residency in the requested country or other documentation). This can be provided at https://nvc.state.gov/inquiry. In limited circumstances, NVC may need to contact you for additional eligibility requirements. Note that transferring your case might not result in immediate processing as cases are processed in order based on the date the case became documentarily qualified.
-If you are requesting a transfer for a K Visa, the receiving Embassy or Consulate has the discretion to approve or deny the acceptance of a K visa application from an applicant outside the consular district. Contact the potential gaining U.S. embassy or consulate in writing to request a transfer of your case and include the reason for the transfer request. If you paid the MRV fee at the original post and the transfer request to a new post is subsequently approved, a new visa fee will be required.”
Source: https://travel.state.gov/content/travel/en/us-visas/immigrate/national-visa-center/immigrant-visas-processing-general-faqs.html
So you would need to wait until the petition is approved by the USCIS.