UX Related Question

Hey, I’ve been working on a shooter game lately and I’m not using roblox’s backpack
But some of the feedback ive been getting is that players dont realize that they can use 1-3 to change their guns

To me it seems fairly obvious but apparently it is not

Now my question is;
How would I make it so they know thats an option without using roblox’s (tedious) backpack or anything similar (I’d like to have the screen as clean as possible during play time)