Hi @Anonymous ,
Do you want to update the same time from powerapps to sharepoint list?
The key point is that the time zone in powerapps and sharepoint list is different.
Time zone in powerapps is local time zone and could not be changed.
Time zone in sharepoint list is one setting that you need to set in site settings.
So the most simple way is to change time zone in sharepoint list to your local time zone.
You could check your time zone in powerapps like this:
-TimeZoneOffset()/60

In my example, my time zone is utc+8.
In sharepoint , you could set time zone like this:
site information->view all site settings->regional settings->timezone


You just need to change this time zone to the time one in your powerapps.
Then time zone in powerapps and sharepoint will be the same. You could directly use time in powerapps to update to sharepoint list, no need any transferring.
If you want to use utc time to update to sharepoint list and display as utc time in sharepoint list too, you could set like this:
1)in powerapps transfer time to utc time to update:
DateAdd(Now(),TimeZoneOffset(),Minutes)
// transfer now() to utc time
2)in sharepoint list, change time zone to utc.
3)display this time field in powerapps, use this formula to display:
DateAdd(ThisItem.timefield,-TimeZoneOffset(ThisItem.timefield),Minutes)
//transfer utc to local time zone
Then in powerapps, you will always view local time zone. In sharepoint, you will always view utc time.
About transferring time, please refer this:
https://docs.microsoft.com/en-us/powerapps/maker/canvas-apps/functions/function-dateadd-datediff
Best regards,