This e-mail may have ended up in your spam folder. Therefore check in your spam folder if this e-mail is here. With a Gmail account, the spam folder is in many cases a "hidden" folder, so there is the experience that the mail has not arrived at all.
A possible solution is to perform the search "label: spam jobapp" in Gmail in the search function. After this the mail will most likely be visible.
Check with your supervisor for cancelling an offered or accepted shift.
No, you can't. The system will select available colleagues for new replacement requests, which will fulfill the company policy. These selected colleagues will get a request to volunteer for your shift.
The functionality "Shiftreplacement" is not on by default for every store.
By status changes you can see what is happening with your replacement request. As soon as you have requested replacement, you see the status 'Requested' next to the shift. When at least one colleague has accepted the request, you will see the status 'Pending'. If your manager approves the request, the shift will be removed from your schedule (and the selected colleague will get the shift). In case the manager rejects the reques, you will see the status 'Rejected'. Also when the replacement is no longer possible, you will see the status 'Rejected'.