It depends on what type of 1099 you'd like to enter. There are many, and they are reported in different places. Investment income is common, so here is how to enter a 1099-INT:
Under "Let's import", choose "Enter a different way."
Choose Interest, continue
Choose "Type it in myself"
Enter FEIN from payer, payer's name, and amount of interest. Choose recipient's name from dropdown box.