Do you need to show how the modal verbs change in Reported Speech in a single handout? Here's a grammar guide which summarises the changes in modal verbs in Indirect Speech. In the guide, there are mainly two categories, which distinguishes between the modal verbs that change from the modal verbs that stay the same. It'll simplify the changes in modal verbs and will help your students remember them while producing an Indirect Speech.
You can either use it as a grammar reference handout and go through it with your students or just place the second handout on classroom walls as a reference point for future lessons.