Edit and Use

Your remote has two modes: Edit for changing it and Use for tapping buttons to do things. Switch with the Edit / Use buttons at the top.

Tap Edit at the top. The little screen on the remote says EDIT.
Tap any button on the remote. Its settings open in the Button panel (below the remote on a phone, beside it on a computer).
Tap + on an empty slot to add a new button there.
Drag a button onto another slot to move it there; if that slot has a button, the two swap.
To delete a button, select it and tap Remove at the top of the Button panel.
Tap Use when you're done. Now tapping a button does what it's set to do.

Good to know

Everything saves automatically to your account; the top bar says "Saved to your account".
On a phone, a small copy of the remote stays pinned at the top while you scroll the settings. Its arrows step to the previous or next button.