How could you fill up a dried out river?

Like from a dried out river, to a full one. IN THE DESERT.

Even in a desert, "Dried out river" says that there was once a river there but something has changed in the source of the water or the weather pattern to eliminate the supply. To reverse the process you would have to determine what has changed and why, then change that back to the way it was before the water source dried up. Even that may not completely restore the area because typically once the water is gone, the topsoil blows away in the wind.

In the name of "progress" many areas have diverted rivers, built dams, destroyed vegetation and mis-managed crops in ways that have long term negative environmental consequences.