You don't need a specific tutorial for that, you can just cut out an area of the back of the crown corresponding to the shape of the letter.
You can do it with a simple
clipping mask (a path that hides everything in a group except for what it covers). This works no matter what type of image the crown is or how complex it is.
- Position crown and text. Put the crown at low (40%?) opacity in the
Transparency window so you can see the text underneath
- With the pen tool, draw a path that surrounds the crown (doesn't matter how far by), then carefully comes in around the part of the text you want to see uncovered. So the crown is completely covered up, except for the bit you want to disappear so you can see the text behind it.
- Put the crown back to full opacity, make sure the new path is on top (
Object > Arrange > Bring to front).
- Select path and crown,
Object > Clipping Mask > Make.
You can double-click into isolation mode on the clipping mask to change or move the crown inside it, and the clipping mask itself is a regular path that you can edit the normal way.