Mohamed Mazhar

Hello Mohamed,
I assume you mean the application Affinity Photo. I also assume you mean the top level menu, File, New Focus Merge.
If these assumptions are correct you can add/modify /delete keyboard shortcuts by clicking (in the top level menu)  Edit, Preferences,, then click Keyboard Shortcuts,

Scroll down a little and you will see that New Focus Merge has no shortcut. 

Pick something you like  (shift N in my sample)  ..

and click the Close button. Done...