Reading the article, it's not clear to me how this will "weaken the impact of Trump's tariffs".
What was decided in the meeting?
The countries' three trade ministers agreed to "closely cooperate for a comprehensive and high-level" talks on a South Korea-Japan-China free trade agreement deal to promote "regional and global trade," according to a statement released after the meeting.
"It is necessary to strengthen the implementation of RCEP, in which all three countries have participated, and to create a framework for expanding trade cooperation among the three countries through Korea-China-Japan FTA negotiations," said South Korean Trade Minister Ahn Duk-geun, referring to the Regional Comprehensive Economic Partnership.
Sure, this meeting will help RCEP, but all three countries are heavily dependent upon the US consumer base. Increasing trade amongst themselves will not compensate for the reductions they face if they don't cooperate with Trump.