How do you automate your DCA process? (TD Ameritrade users)

I have been using TD Ameritrade for a couple of months. Quite an affordable platform as far as platform fee and additional charges are concerned. However, as someone who wants to adopt a set-and-forget strategy, I can't seem to find a way to automate the depositing and purchasing process. My ideal goal would be to giro in a fixed amount every month and have the system purchase VOO and KWEB according to the amount I depositEd (The unit will of course not be a whole number). Anyone has experience doing so?

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Thanks.