So first go into youre projects settings and add the input Q weapon switcher.
Then create a boolean variable . When you press Q do a branch from the event. Check the boolean value. Then draw that weapon based off the value eg sword is equal to true, gun is equal to false. Once weapon is drawn you need to set the bool variable again so it might be best to make it into a custon function
Eg you start with sword bool = true
You press q it switches to gun then changes bool to false
You press q it switches to sword then changes bool to true etc etc
If you want multiple weapons more than two then give each weapon a variable value eg int so sword is 1 , gun is 2, knife is 3
then use the switch on int node to cycle through