This is really simple.
my idea would be to create some sort of 'HQ' bulletin board for instance,
under the command, "action button"
then, choose to show text,
'Where would you like to go?'
Show choices....
(the names of you places)
now we'd have to use conditional branches here so it's advisable to have say, a key item obtained from a mission or certain place,
e.g:
ticket.
Now,on each choice you'd neeed to set a conditional branch for,
"Item is in inventory"
thus bein the ticket or whichever item you'd choose.
If the ticket is in the inventory you can set to travel to that location.
If it isn't, then you could say something like, you need such and such to go there, or you haven't visited so and so yet.
It doesn't have to be a bulletin board, it can be anything as long s you make it from a new Event Command option. If you need anymore help, reply here/
always liek to help./