Enter the Expense via the Property > Linked Expenses.
Select Create and Link a New Expense
Complete the details of the expense, making sure Tax Deductible is selected, then click Done for the Expense information.
If you have completed all the relevant information for the property, then click Done again.
Once done, the software will deduct the expenses from the rental income when calculating the income tax due. You can view this in Year View > Taxes.