On iPhone, you may need to tap the ellipsis (…) button on the top toolbar to show the “Edit” button
Essentials
Drawing
Use Apple Pencil, a supported stylus, or your finger to draw, drag and drop objects onto the canvas
Tap the Markup button on the top toolbar on iPad and Mac to show the drawing tool picker:
The drawing tool picker can be moved anywhere on iPad by dragging it over to your desired side. It can also be automatically hidden while writing to give you more space on the canvas.