How can I pre-fill the form with current member data who already?

i would like to  enter  the fields  i have and contact them for the rest

Please check this guide: Prepopulating fields to your JotForm via URL parameters

I believe it explains everything that you need. You can also use the app to generate a pre-populated form: http://prepopulate.jotform.io

Let us know if you need any help. Thank you.