TurboTax does it for you when you enter your T-slips.
Your employee-paid premiums for private health services plans should be on your T4 Box 85 and on your Relevé 1 Box 235. The amount shown in Box J of the Relevé 1 is the portion paid by your employer (which could be the same amount but this amount is deductible only in Québec).
When entering your T4 (Box 85) and Relevé 1 (Box J + Box 235), TurboTax will automatically transfer your contributions to your total medical expenses.
Please note that you will not see these amounts in your medical expense receipts but rather at the bottom of the MED & QMED worksheet (available only in the CD / Download version) and it will be included in your total medical expenses used to calculate the credit. Line 330 of Schedule 1 (CRA) & line 36 of Schedule B (Québec).