Amit, this is something in one of my scripts ... but I don't have much familiarity with it, so might not be what you're looking for. (NOTE: function includes cases for some other response types which you haven't asked for)
function responseToText(itemResponse) {
switch (itemResponse.getItem().getType()) {
case FormApp.ItemType.CHECKBOX:
return itemResponse.getResponse().join("\n");
break;
case FormApp.ItemType.GRID:
const gridResponses = itemResponse.getResponse();
return itemResponse.getItem().asGridItem().getRows().map(function(rowName, index) {
// Logger.log(rowName);
return rowName + ": " + gridResponses[index];
}).join("\n");
break;
case FormApp.ItemType.CHECKBOX_GRID:
const checkboxGridResponses = itemResponse.getResponse()
return itemResponse.getItem().asCheckboxGridItem().getRows().map(function(rowName, index) {
// Logger.log(rowName);
return rowName + ": " + checkboxGridResponses[index];
}).join("\n");
break;
default:
return itemResponse.getResponse();
}
}