There are many ways to do this.
You could use separate menu items for triggering separate tabpages, and each menu item would have an Enum property and value set. Then in the run() of your form you could check for the element.args().parmEnum* and switch to the tab you desire in X++.
Other solution is to pass in the current form in your args.caller(element), and in the run() again based on your element.args().caller() /which is your FormRun object/, you could do the same as mentioned before, or drive what tab to call by a public method defined on your caller form, saving args().caller() into a variable of type Object, and then call your public method on that variable to retrieve which tab to select.