If your booking at booking.com is flexible to cancel it without charges i recommend to cancel it and to contact direct to the hotel to make you an offer fo 1night stay including PCR test and transfer.
Otherwise if your booking is non-refunable contact through booking.com messages with the hotel and request to prepare you an offer for the PCR test and the transfer that you pay it to be confirmed after to the Thailad pass.
Ask the invoice to iclude the 1night stay plus PCR test and transfer prepaid