I believe you just fill out the transcript tab of the OMSAS application and it automatically gets requested when you submit the application. Also, I THINK it's okay to submit on Oct. 1 as this is from the OMSAS website under Transcript Requirements - Online Transcript Requests:
" OMSAS must receive your online transcript request by October 1, 2020, to satisfy the transcript deadline requirement. "
From my understanding, you just need to request your transcripts by Oct. 1. However, this is my first cycle applying so please correct me if I'm wrong and any other insight is welcome!