How to convert the date format - From DOUBLE to Datetime in KIbana elastic search

Could you please help with the below issue.

Is there anyway can we change the date format for the below mentioned columns?

Time_token : 1.6013861887237842E9

Created_at: 1.600254825E9

I want to create the dashboards by using the above date column but unable to develop it due to format issues

What is that field mapped as? Unless it's a timestamp, you will struggle.

It is mapped as string and showing symbol #