If you are the account holder or authorized user, you should be able to log into the privacy center and delete all the account data.
https://www.intuit.com/privacy/
Note this is permanent. A less drastic measure, in the event that you ever need the person's tax data for any reason, would be to lock the account. A locked account preserves the data but can't be accessed or hacked unless you call customer support to unlock it. You need to call support to lock the account, too. You will only get a phone number from the contact page during business hours, and you need to be logged into the account in question to get routed to the right person. If you can't log in to their account, select that you are using a desktop program to get to a person to help. You will need to provide proof of identity and that you are the authorized representative of the account owner.
https://support.turbotax.intuit.com/contact/
There is no chat robot as far as I know. This site is not chat, but a bulletin board where volunteers try to help. Also, don't google Turbotax's customer support number, since scammers can buy ads and get you to call them and pay them money. Use the secure web form to get a contact number.
If you use the privacy web page to delete the account it should remove marketing emails as well. If you lock the account, you may still get marketing emails but you can delete them, unsubscribe, or ignore them. But be careful not to ignore or delete any emails that are being sent as part of any effort to prove you are an authorized user of the account.
