Hey Hongjie
I think this is a workflow related ask.
There’s a few ways to do this 
- EpochDate Time is milliseconds since 1970, therefore you can use a transformer to increment a date starting from 1970-01-01 and add the milliseconds, like below, but passing the epoch time rather than hardcoding like I did in the screenshot
You can also take into account locales/timezones and specify an output format:

- Write a node.js action (instead of a CLI connector) and put in code something like this:
var request = require ("request");
module.exports = function(){
this.id = "my-first-action";
this.label = "Sample";
this.help = "Sample code for reference";
this.input = {
"title": "From Epoch",
"type": "object",
"properties": {
"epochDateTime": {
"title": 'epochDateTime',
"type": 'integer',
"description": 'epoch/unix date/time',
"minLength": 1
},
}
},
this.output = {
"title": "output",
"type": "object",
"properties": {
"isoDatetime": {
"title": 'iso Date/Time',
"type": 'string',
"description": 'date time in ISO format',
"minLength": 0
},
}
},
this.execute = function(input,output){
if(input.epochDateTime){
var date = new Date(input.epochDateTime);
return output(null, { "isoDateTime" : date.toISOString()});
}
}
}
- Write the same but as a CLI connector.
- You can do similar as option 1 in a Flow Service.
Clearly the first option is the most simple 
If you ever need to go the opposite direction then CalculateDateDifference can be used, to calculate the number of seconds between 1970-01-01 and the datetime, then multiply up to get the milliseconds value with another transformer.
Some people might find this easier in a FlowService so just for completeness, I attached a couple of FlowService samples exported from wm.io integration to convert an Epoch date to Excel formatted date (the excel format date always blows my mind
), and also a convert date time to Epoch.
Just remember sometime epoch has two flavours to content with just to make life difficult - seconds or milliseconds 
convertEpochDateToExcel.zip (8.4 KB)
dateTimeToEpoch.zip (8.3 KB)
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