IRS website says that I will receive a 1099-INT from the IRS for interest on 2019 refund. Did not received a 1099. Is the payment still reportable?

Yes.  

You should be reporting all interest income even if your institution does not send you a Form 1099-INT.

You will enter your Interest income as follows: 

1. Select Income & Expenses under the Federal Tab 
2. Scroll down to All income
3. Select Interest on 1099-INT
4. Select Add another 1099-INT
5. Proceed to enter in the applicable information

If you do not know the amount of the interest income, you can view your account with the IRS using the link below.

IRS Account information

I received this interest income from IRS in August 2020. But I did not receive 1099-INT from IRS. I am . I am trying to manually add the information by following the steps you mentioned. I have a couple of questions on what to enter. 

1. What should I write in the 'Received From' box?

2. I did Married filing Jointly for my 2019 tax returns. There is a question where it is asking me if this interest income belongs to myself, my wife or both of us. What should I enter there?

1.  Enter IRS Interest or US Treasury, it's not very important 

2.  If you filed a Joint return it belongs to both of us.