where do I put returns and allowances on schedule c, part 1 Income, line 2?

as you are going through the business section you should come to a page where you come to a page "Enter Business Income That's Not on 1099-NEC or a 1099-MISC/ there you'll find a line for returns and allowances.

In order to populate a figure on your Schedule C line 2 for returns and allowances, here is how to enter the information in TurboTax Online:

1. Navigate to Federal > Wages & Income > Self-employment income and expenses 
2. Edit your business
3. Scroll to Income, then select Add income for this work
4. Choose Rebates and refunds, includes any income returned to customer
5. Briefly describe the amount- "Refund" or the like is sufficient and enter the amount

my screen selection ends at uncommon there is no rebates and refunds for selection and Im using premium online tax

Have you entered any Income for your Business?  If you haven't, that may be why your screen is titled 'Let's enter the income for your test work' instead of 'Let's enter any additional income ..'.

If you enter some income by clicking the appropriate category and enter an amount, you should then get the correct screen.

@ysalim 

i went ahead to proceed by selecting the 1099 Nec but then there was no way to find how to enter the return and allowance

When you enter your sales on Form 1099-NEC, you will see an option to enter Income You Gave Back, on the screen that says Business Income. Choose that option to enter your returns and allowances:

@ysalim