If I used buy back OMERS option and contributed to my pension plan, where, in TurboTax, I include this contribution, under RRSP or somewhere else?

Did you get any T-Slip related to OMER pension plan contributions? 

I received Income Tax Receipt for income tax purposes 

In your tax return, you have to enter all tax slips you received. 

As your question is more a tax related question, we suggest you to contact CRA for this question.

Thank you for choosing TurboTax.