My condolences on the death of your son.
No one at TurboTax will be able to help you. As long as your son's return was accepted by the IRS, only the IRS will be able to help you locate his tax refund. See the link below for information on contacting the IRS by phone. Be prepared for a wait, though.
Telephone Assistance | Internal Revenue Service (irs.gov)
*** I am NOT a tax expert. I am a seasoned TurboTax user, and volunteer to provide assistance to TT users. Nothing I post is to be considered TAX ADVICE; I bear no legal liability for responses.***