Copying dataset content to form dataset

HI! I want to set up a form (formdataset 1) on a page where I have an other dataset (dataset1) connected in order to allow users to use one of its colums for the selection in a dropdown. My aim would be to copy all related info in the seleced row from dataset1 to formdataset1 in the background while users are subbmitting the form. Is that possible somehow? Thanks a lot for your help.