Minecraft PE | Insert a cross in the middle?

How can I insert this cross in minecraft pe with which you select the block that you want to destroy, for example?

In the settings. As far as I can remember under graphics. But without it it's a lot better in my opinion.

So first you go to the settings in Minecraft. Then you have to tap the "Touch" section in the settings and scroll down to look for the term "shared control" and now turn the lever around tada