As with many things in Natural, there is a simple answer, and an involved answer.
The simple answer is NO. Natural maps always “tab” geographically, left to right, top to bottom.
The more complicated answer involves programming and potentially re-educating users about how to “tab”.
You can establish a PF key, say PF5, as the “tab key”. After the INPUT statement, you test for PF5. If PF5 has been pressed, you check a variable where you keep track of where you are. You now change this variable and then do a REINPUT using MARK to position the cursor at the next position.
WARNING. This can get very messy. First, the tab key will still work. This means that you probably should read *CURS-COL and *CURS-LINE to figure out where the cursor is, rather than use a “tracking variable”.
Make sure the users are “okay” with using a PF key to tab.