ISCECA is a bilateral agreement between Singapore and India only. Vietnam is not a party under the ISCECA, hence, you would not be eligible to apply for a Form CECA. Alternatively, you may wish to explore using ASEAN India Free Trade Agreement (FTA), to which Vietnam Singapore and India are parties of the FTA, for the import of goods from Vietnam into Singapore and re-export to India. You may refer to the Enterprise Singapore website of the respective Free Trade Agreements for the eligibility requirements for preferential CO application.