You do not need to enter the information from the T4PS twice. As long as you have entered the information from the T4PS, and also that you have capital losses from prior years (and the amount), the software will apply the losses for you.
My losses are 10 years old. I do not think the software has this info. Can I enter it.
CRA will keep your record of capital losses forever and the non-capital losses for 20 years. If the losses are more than 10 years old, you will not be able to import them using AFR, instead, you have to enter them manually.
Search for "losses" using the magnifying glass on the top bar. Choose what type of losses you are claiming. To claim a capital loss against a capital gain from T4PS, choose "Net-Capital loss".
Check this link on how to report capital gains: https://turbotax.community.intuit.ca/community/investments/help/where-do-i-report-capital-gains-or-losses-in-the-online-edition-of-turbotax/00/873778
I hope this was helpful