Within 3 months after the effective date of this Act, the merchant shall file an application (upon a form prescribed and furnished by the Department) to receive a one-time credit for the Use Tax paid on merchandise subject to tax under this Act purchased during the 6 months immediately prior to the effective date of this Act. The Department shall issue a credit equal to the total Use Tax paid in the 6 months immediately prior to the effective date of this Act. Upon the issuance of the credit, the merchant may apply the credit against the tax imposed under this Act.