RC62 slip is not available in my CRA account. what do I fill at UCCB

The UCCB program was discontinued in July 2016 and replaced with the new CCB payment which is not reported on the tax return. (Tax Free).

I am still unable to proceed to file my Tax online because it requests me to fill the RC62 box 10, 11 and 12 for UCCB and i did receive child benefits in 2017.

Canada Child Benefits are not the same as Universal Child Care Benefits. The UCCB program was discontinued in July 2016. Remove any reference for RC62 under the "Income" tab > "T-slips" UCCB. (Unless you can confirm with CRA that you received a lump sum catch up payment in 2017.