Standchart will either send you a letter or an sms with the information. You will have to call them and tell them your instructions.
Do note that oversubscription request is not confirmed and may not be fulfilled subject to the company decision. Only your entitlement is confirmed.
This was the process for one of my stocks when there was a rights issue.
Shaun WQ Lim
06 May 2020
Depends on when Standchart sends out the letter or sms. In my personal experience, the letter takes longer to reach and sometimes is after the deadline. The SC deadline is usually a few days before the underlying stock deadline. Do look for the sms or call their hotline to confirm with them. Their hotline is quite responsive.