Hello Mariahz,
Welcome to Apple Support Communities. We understand that your Hide My Email address has been deleted and you're unable to access your Smartsheet account.
To clarify, is the email address inactive or has it been deleted? If it has been deleted, please be mindful of the following details:
Important: Deleting an address created with Hide My Email is permanent, and it’s deleted on all your devices set up for Hide My Email.
You cannot reactivate the address.
If the email address is inactive, you can take these steps to reactivate it:
1. On iCloud.com, go to Account Settings, then click Manage in the Hide My Email section.
2. Scroll to the bottom of the list, then select an address below “[number] inactive email address(es).”
3. Click “Reactivate address,” then follow the onscreen instructions.
Click here for more details: Stop using, reactivate, or delete a Hide My Email address on iCloud.com
We hope this helps.
Take care!