Macintosh start up disk disappeared when doing a reset

Hey guys, i’ve attempted to wipe/reset my laptop as per the directions on apple through recovery mode. it worked fine the first time however i wasn’t convinced it wiped everything so i made an account and logged back into the laptop, then when i was satisfied i tried to do the procedure again to rewipe as i created an account. however the second time it wiped the macintosh start up disk and there was no disk for me to reinstall os. Any ideas on how to get the start up disk back?! i’m not technology savvy so i follows apples instructions to a T! It is also a Macbook Pro 2015. i had updated it to Big sur before i reset everything too.