Working on 2018 taxes for my son. He contributed $1131.01 to an RSP not an RRSP. Can't seem to find a way to input that into the turbotax software. What am I missing?

Do you mean RPP, Regustered Pension Plan?  This amount should be on his T4 and that is where it should be entered.
(RSP is just a way of saying RRSP).

Actually his slip calls it "Retirement Savings Plan."  

If it’s a non-registered savings plan, then it’s treated like a capital investment. You report the income, and any sales of the assets. There is no tax credit for contributing to a non-registered savings plan, and the income, proceeds of sales and withdrawals are taxable.