The only way to make an entry on Line 229 while using TurboTax Online is through the "Employment Expense" section.
If you click on the Find Icon > Type in Employment > Highlight Employment Expenses > click Go.
Check the box beside "Incurred expenses for the purpose of earning employment income" and Continue.
Check the box beside "Other Employment Expenses" and Continue.
Make your entry in the box "Other Expenses".