I left the date part blank but filled the rest of the GP details, as my DD had never been to the GP either, only for jabs.
HV referred her to peadiatrician/SALT. Infact when I did ring the GP once for help with a referral to the ND team as I wasn't getting anywhere, they said I'd need to go back to who made the referral. So no help from the GP.
If your super worried you could add on the extra info part - no date given as GP not involved.
There are other questions that ask about professionals involved, so you can cover why the GP isn't involved through those.
I will say I'm still waiting to hear on DD claim.