It is not possible to change the billing country default in LCRM. You will need to set the billing country default on the Luminate Online donation form being used to process the donation in LCRM. Follow these steps to change the country default:
  1. Log into Luminate Online
  2. Navigate to Fundraising, Donation Management, All Donation Forms tab
  3. Find the donation form and select edit
  4. Choose Step 3, Design Donor Screens
  5. Edit the Donation Form
  6. Select Billing Country from the right hand column
  7. Go to Step 5, Pre-Selected Country
  8. Choose the country you want
  9. Click Save

The chosen country will now be the default country if that form is used in LCRM. If you want this country to be the default for all donation forms, repeat the above steps on all donation forms.