I'm not following. Are you saying when you tab out of the last subform datasheet you want it to go to the next record on the same datasheet? As far as I know, you cannot do that for datasheets without code (such as setting focus to a control with zero width and coding to shift the focus to where you want). Apparently, CTRL+TAB will allow you to jump out, but that's probably not intuitive to your users. To get to the next record, use the enter key and ensure the option for enter key navigation is set in the database Advanced Properties. If I didn't already mention it, I'm not sure what your issue is
The more we hear silence, the more we begin to think about our value in this universe.
Paraphrase of Professor Brian Cox.