Set the async function evaluate result to CalcEngine, CalcEngine will use this value to recalculate the cell that contains this async function and all dependent cells.

var instance = new GcSpread.Sheets.Calc.AsyncEvaluateContext(context);
var returnValue; // Type: any
returnValue = instance.SetAsyncResult(value);

function SetAsyncResult( 
   value : object
) : any;