My spouse died in August 2018 and did not need his age exemption. Turbo Tax will not allow me to transfer the exemption to my tax return. How do I do it?

Sorry for your loss.

Are you preparing a "coupled return" (both return at the same time)? Or are you preparing separately? 

Generally, you need to prepare the returns separately in the year of death. On your return, you will need to indicate your marital status as Widowed, and a marital status change (where the date of change is the date of death).

If you are in forms mode, you can search for Schedule 2, and enter the transfer amounts there. If you are in the interview mode, under the Easy Step, under Deductions and Credits => Other Deductions Profile, checkmark "Federal and provincial transfers from your spouse". Enter the amounts accordingly.