I had a one-time income of $400 for an administrative help which is not related to my business. Where and how can I claim such income?

Thanks for your question. you could enter that amount in the other employment income section. Please follow the instructions below. 

1. Select the icon of the magnifying glass (or Find) on TurboTax, and type Employment.
2. Select Employment Status from the options that appear, then select Go. The Employment Status page appears.
3. Select Received tips, gratuities, occasional earnings, or other employment income from the list, then select Continue. The Other Employment Income Sources page appears.
4. Enter information about your other employment income, then select Continue.