Congress writes laws directing that designs of coin and currency be changed, Treasury decides the final design for artistic and technical reasons subject to specifications dictated by Congress.
The Obama Treasury announced in 2016 they "wanted" Tubman on the $20, but I can't find any law that Congress passed to approve the change. Executive branch (Treasury) can't implement this on its own without lawmaker approval.
This is more bait to get the people fighting among themselves.
The last paragraph of this NYT Trump-hate diatribe alludes to the fact that Congress has never authorized the change. I can't find that anyone has even written a bill to be voted on.
'“At Women On 20s, we’re not surprised that Secretary Mnuchin may be kicking the design reveal of the $20 bill to sometime beyond the potential interference of a Trump presidency,” the group said in a statement calling on Congress to pass legislation to add Tubman to the currency. '
It's all bait. Don't fall for it.
https://www.nytimes.com/2019/05/22/us/harriet-tubman-bill.html