A huge hurdle for American manufacturers is that their products simply cost too much, all else being equal, because the value of the dollar is too high.
So their plan is try and devalue the dollar while also keeping it the reserve currency. To put that another way, he wants countries that have invested in the dollar to take a hit on their investments while also getting their population to buy more American goods.
His negotiations will probably center around offering continuation of "America world police" services (people hate it, but governments love it) in exchange for following this path.
Whether or not this will work? Who knows, but at least that is the idea they have chosen.