How to covert int to hex type value and save it in a string?

[rextended]

You do not notice the request from @rrwakc on previous post? :))
https://forum.mikrotik.com/viewtopic.php?f=2&t=57665&p=869033#p868885

I do not know why need that, but is for convert single word signed hex to integer

0xFF85 to -123