There are about 700 Haitian's per sq mile of Haiti though to many are consolidated.
They need to spread out and in doing so they can nurse the land back.
Food, Clothing and Shelter are primary and of course Medicine comes into play with such a sick level of the people.
Shelter requires material, and they have plenty to get started in terraforming, as it's what they used to make the tinroof city that needs to be dismantled anyway, to make room for vegetation where its really needed.
Single story construction that can reasonably withstand hurricans, water and even earthquakes. Such construction that will not be so life threatening upon failure and easy to rebuild. Pyramid/angle style wall construction perhaps from the rubble of the earthquake We didn't always use cement block construction but have used stone. Such shelters are not intended to last but moved as needed.
Food and clothing is where the worlds donations can work until the land starts providing.
Seed of the quality that can withstand the current conditions while mainly providing the land with roots to hold the soil and begin the process of generating new top soil. Secondary to this is of course to produce food for the people. Human waste management needs the technology to turn human waste into land healthy fertilizer. We have this technology.
Water reservoirs built to catch and store rain water that will most certainly come.
As the people migrate outward from the dense population, transportation of resources will also evolve, creating, repairing or upgrading roads.
This is about restoring the land first from which the people will then be able to repair themselves.
The manpower is there, the resources are there enough to move in the right direction, knowledge may be lacking from within the Haitian people but we the world certainly have plenty.
This only a general picture, but it can be done in a few generations.