first the use of the find () function only looks for the first value, it is designed to limit a single query.
the find function is designed to query the id that corresponds to the primary key you want to search
by which a query should be made in the user table where I look for the name of daniela and use a foreach
public function asignar(Request $request)
{
$valor = $request->valor;//donde obtiene el dato "daniela"
$consulta=usuarios::where('name',$valor)->get();
foreach ($consulta as $value) {
$userad = usuarios::findOrFail($value->id);//limite de un registro
$userad->asignacion = $user->usuario_ad;
$userad->save();
}
return redirect()->route('cuenta.tareas')->with('success','Registro actualizado satisfactoriamente');
}