Change date + time in file

Hi, 

I am very new in powershell, I hope someone will help me:

I have a file in C:\tmp\appFiles.appcache

Which contains:

--------------------------------------

I need to make a script to change date  + time to actual time

For example:

CACHE MANIFEST
# Version: 2019-01-19T13:55:08.3070330+01:00

# Use from network if available
NETWORK:
*-----------------------------------

Thank you for any help