You do not need to submit ESIC half-yearly returns online, as the ESIC website is designed in such a way that you can generate half-yearly returns based on the monthly returns filing. However, if you have more than 40 employees, you must upload the Chartered Accountant Certificate. To do this, please use the SELF CERTIFICATION link on the ESIC website.
Regarding employee entry and exit, your monthly filed returns will take care of this.
Regards,
Mohan.