If you're talking about Schedule C (self-employed) supplies:
1. Click Federal on the left-hand side
menu.
2. Click Income across the top.
3. Scroll down to Self-Employment and
click Show more.
4. Click Start or Revisit by Income
and Expenses.
Either scroll down till you get to Supplies, or click Add expenses for this work.
If you're talking about a Schedule E (rental):
https://ttlc.intuit.com/replies/7404373