All you need to do is create a new icon inside of top bar plus
It’s pretty simple and you can just create something like this:
Icon.new()
:setImage(1234567) -- use any image assetid that you want
:modifyTheme{"IconImageScale", "Value", 0.65} -- update the size if you want
:bindEvent("selected", TopbarFunctions.ShowInventory) -- you can set it to any function
:oneClick()