eval t=strftime(strptime(<your datetime field>, "%Y-%m-%d %H:%M:%S"), "%m/%d/%Y %H:%M:%S")
You can convert your field to epoch then to desired format with something like this:
| eval epochtime=strptime(your_current_time_field, "%Y-%m-%d %H:%M:%S")| eval desired_time=strftime(epochtime, "%m/%d/%Y %H:%M:%S")
eval t=strftime(strptime(<your datetime field>, "%Y-%m-%d %H:%M:%S"), "%m/%d/%Y %H:%M:%S")