Are you asking to show another flag randomly, or in a specific order?
Randomly is pretty easy. You should be able to set the sort option for your detail screen to Random, and then instead of a button to increment a value, you instead create a button with a reshuffle action.
I agree that previous/next functionality should be built in, but I have no idea why it isn’t. Assuming the data in your flag table is pretty static, you could have a column with a number given to each row. Then I would create a new table to function as your tab. It would have a single row with a user specific number column. Then you would have a single relation column that links that number column to the number column in the flag table. Then add lookup columns to retrieve each column you need from the flag table into your new tab table. Then you can build the screen on the new tab the same way as you have it above, but now you can add increment buttons that will increment that user specific number column. When you increment the number, the relation and lookup columns will update with the matching data for that number, which will update the screen.
So in the end, your screen is always pointing to that one single row, but by changing the number it give the appearance of navigating with previous and next buttons, but it’s only retrieving different information for each flag based on the number column that you changed with the increment.