If you want to add or subtract days from any Date Input Field value, you can do this as described below. This sample is using a Date Input Field with only the Name set to ‘Date’ (no Group name defined).

Value for showing the Date Input Field (formatted):

{{ formatDateTime(field('Date').value, 'LL') }}

Value for showing the Date Input Field + 5 days (formatted):

{{ formatDateTime(field('Date').value.setDate(field('Date').value.getDate() + 5), 'LL') }}