How can we prepopulate a Date Field within an Issue Custom form with today's date?

Hi @anasooya - if you just need a field to indicate "today's date" when an issue is created you can use the "Entry Date" in reporting, or if you need it visually in-line with other data in a custom form you can create a calc field with a date format and just have the calc be {entryDate} . 

If you still needed it to be adjustable afterwards you could then add an override field with an if/then in the calculation.