I need to enter "Work-space-in-the-home expenses" on line 22900, how can I do that?

You would enter those expenses into the Employment Expense section. To get to the Employment Expenses section in TurboTax Online:

1. Select Find in the upper-right area. (The Find button becomes visible after you have completed the Introduction/Profile section.)
2. In the Find window, type “employment.”
3. Select Employment Expenses from the list of results, then select Go.