Substitute @user@ for @target@ in same command line

[TheHaruFenix]

I have this:
Cmd name: !test1
Cmd Msg: Hello @user@/@target@


I need anyway to make this example in chat:
User1: !test1
Bot: Hello @User1
User1: !test1 @User2
Bot: Hello @User2


In other words, i needed to figure out a way of bot to switch @user@ to @target@ if the command user has put a @target@ before the command...
Anyway? @if@? I dnt know

[TheNumbLock]

@if@[@target@||||Hello @user@||Hello @target@]