Here is the link to the Absentee Ballot Application Web Portal from the Tennessee Secretary of State’s site. It lists the qualifications and instructions.
You can monitor the status of your request by using the HCEC Voter Request form:
Here is the Absentee By-Mail Ballot Request for the upcoming August 6th, 2020 election. Note that the last day to accept a Request is July 30th, 2020.