Should I add the amount paid to me while on medical leave to the amount in box 12a?

[jmtrbotx]

It is marked as “Third party sick pay”.  Should this be in box 14?

[SharonD007]

No.  Enter your W-2 exactly as you see it.  Don't change anything or add amounts to other boxes.  The information that your employer lists in box 14 of your W-2 doesn't affect your income tax return, but you should enter it when you are inputting your W2 data.  TurboTax provides you with a dropdown menu of codes you can choose for your W-2 box 14 entry.  If what’s in box 14 doesn't match a dropdown code, select Other for the code in box 14. 

For more information, ‌ review the TurboTax article What's box 14 on my W2 for?  and How do I fill out the box 12 information from my W-2?