Honestly, I dont use thats app on the BB itself. Your carrier has a special website for that. I'm going to assume that you are in the Good Ole US of A so the 9700 is only for ATT or T-Mobile.
I have a 9550 and i use there website to edit all of my Email accounts. They are actually going to upgrade to BIS 3.0 this week end.
These website should help depending on your carrier
go to options, advanced options, then locate host routing tables, hit menu and select register now, now go to your applications screen and open the setup folder, and click on the manage internet email option, on this screen you should see all the emails accounts you have set for your device, highlight the one you want to edit, click menu and select edit, that will give you the options not just to set folders but to edit sync, signature etc...