If you have already done one amendment online for PSLE sec1 posting exercise and want to do one more, you need to visit the school and do it. I just did it in the morning and thought that it will be useful if I share this with you.
Ref: moe website sec1 posting exercise FAQs
second amendment for PSLE sec1 posting exercise?
Unlike entry to Primary Schools, admission into Secondary Schools is based on meritocracy. PSLE results are used as key admission criteria. Discuss everything related to PSLE and selection of Secondary Schools here.