Hi,
You would declare the drawings in box 98, on the supplementary page SA103F page SEF5:
Self-employment (full)
If you are completing an online tax return, you would tick 'yes' to the box asking if your have an annual turnover of more than £90,000. By doing this, you have the full self employment page. Tick 'yes' to the option to include a balance sheet. Enter the drawings in the last box on page 2 of 2 of the balance sheet.
Thank you