Odoo - Can't Change Default Currency Company

I want to change the company currency by opening Setting->Companies->Currency. But when I already change the currency and hit save button, I get this warning dialog

You cannot change the currency of the company since some journal items already exist

How to solve this problem?

You cannot change the currency of the company since some journal items already exist

• Some data are already created with the same currency, if you do not need that entry then simply delete it and then change the currency.

reference code - Source Code

#forbid the change of currency_id if there are already some accounting entries existing
if 'currency_id' in values and values['currency_id'] != company.currency_id.id:
    if self.env['account.move.line'].search([('company_id', '=', company.id)]):
        raise UserError(_('You cannot change the currency of the company since some journal items already exist'))