Convert UNIX dates to regular dates to import in FileMaker

My original post was a request to convert with applescript UNIX dates to regular readable dates to import in Filemaker pro.
In reference to https://macscripter.net/post.php?tid=45408
Many people helped, and the scripts worked fine, however since I moved to Mojave none of the scripts to convert UNIX date to regular readable date is working anymore
Also, the app changed it’s format and is now a plain text file with several “records”

The text format is as follows

Timestamp:1553116270 (CR)
createdAt:1344552292 (CR)

“§” I added to the texty file to separate the various records

I hope to be able to select the text file
convert
Timestamp
createdAt
and save in a a different file of choice

Using the internet I got these results:
Timestamp:1553116270 = Wed, 20 Mar 2019 21:11:10 GMT
createdAt:1344552292 = Thu, 09 Aug 2012 22:44:52 GMT

which would be fine for my work

How can I save the text file to another textfile of choice?

Thanks a lot

Dan

Model: IMAC 2017
Browser: Safari 537.36
Operating System: macOS 10.14