Doing my 2018 Tax, I found wrong reporting with my 2017 Tax. The capital G/L for a T5008 strip was wrong which is resulting a missing capital loss carry. What should I do

You'll need to either make an "adjustment" to your 2017 tax return or "ReFile" it. If you want to use the Net Capital Loss incurred from this adjusted T5008 entry on your 2018 tax return, you will have to wait until CRA processes the adjustment and issues you a revised NOA (reassessment) stating how much of a Net Capital Loss you have available.

https://turbotax.community.intuit.ca/replies/3639538