There are two ways to unsubscribe from receiving push messages from the game.
If you only want selected type of push messages, you can set it up through the game settings.
Game Settings (Cogwheel) > Push Notifications > Push Settings > Turn off messages for selected types of messages
If you do not want to receive any type of push messages from the game, you can turn them off entirely through your device settings.
Go to your device and/or app settings and turn off all notifications from Homerun Clash.
Doing so will disable all messages from the game even if you have them 'ON' in the game settings.