Its not that easy. But you can do it this way:
Create custom game -> Change your Q Ability to Space key (camera snap) -> Press Okay -> and change it back to Q again.
Then: Leave the game -> Open your Riot folder -> open Config folder -> make a backup of input.ini and PersistantSettings.json
Then: Open PersistantSettings.json -> Unter the line "GameEvents" and "Settings" you can see "name": "evtCameraSnap" -> Change "evtCameraSnap" to "evtPlayerAttackMoveClick" -> One line below change "value": "[<Unbound>]" to "value": "[Button 1]" -> save the file
Then: Go to Input.ini -> Remove all Events and write: evtPlayerAttackMoveClick=[Button 1] -> save file and done.
Here is a link to a video showing all these steps:
https://www.youtube.com/watch?v=RNYV5g3PbAsThis should work now =) hope you can do it