I believe you can set the selectedIndex of the controller. Try [myTabBarController setSelectedIndex:myInt];
If you are using a segue, you should set that in your prepare for segue method. Here's an example.
- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender
{
if([segue.identifier isEqualToString:@"myIdentifier"]){
[((UITabBarController*)segue.destinationViewController) setSelectedIndex:myInt];
}
}