if they're team galactic you have to beat them with Pokemon over lv. 70
if they're not team galactic then you have to go the survival area and talk to Buck then go back
if that doesn't help then you have to go inside the battle frontier and challenge a facility and whether you win or lose heatran should be avalable.
Hope this helped!
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you need to fight them to get past
you battle them
your game has glitched then cause right after you get giratina you should be able to go to sunnyshore city
Nothing evolves into heatran, heatran does not evolve!