It does not work that way. Since it's not trivially readable, the structure of the file is unknown (and the file extension ".dat" does not imply the structure).
In order to manipulate the file to extend a use time, the program using this file needs to be reversed. So it can be seen how the file is read and the information is processed. Then the file can be altered to pass other information to the program.
However, if that is not a crackme, I guess it's considered warez which is against the rules here.
With best regards
Jeoni