I just tried the TOS-Web version, but it too has no mention of "Cash-Secured Put".
It seems to have not even the said "Custom" selection of the TDA web, if I'm not mistaken.
You are not going to find "Cash-Secured Put" as a specific option in a drop-down menu or whatever in the trading software. As @Sergio123 and the customer service from TDA have pointed out to you, it's just selling a put. So if you want to do a "Cash Secured Put", you just need to go to the trading software and open a short position in puts while ensuring you would have enough money to buy the underlying if you ever get assigned. That's essentially what a "cash-secured put" is, short put position secured by enough cash to finance any possible assignments.
