In order to enter an assessed loss, choose source code 4000 as indicated on the screen below and enter the other information description nature and the assessed loss as a negative amount.
Sars carries the assessed loss amount therefore we don't send it through. It is only used for the purpose of calculation.
This is what the screen should look like once the assessed loss is entered.
The Income Summary is indicated below. Note that the assessed loss is for illustrative purposes.