Hmm, I assume we're talking about the Interface record picker element? If so, your URL should look something like this:
https://airtable.com/appidKyaHdNiJi3fU/pagCK29CZjYhUV4Tu?dIY2l=reclibWXTsBGFBsHH
And so it's:
https://airtable.com/APP_ID/PAGE_ID?RECORD_PICKER_ELEMENT_ID=RECORD_ID
And so you should be able to prefill the specific record picker element ID by modifying the RECORD_ID value