You're receiving no answer because we don't know. Our sources for the ancient world are limited, and we only know what they tell us and what we can supplement through, for example, archaeology. It's a common problem on AH (and with high school students and undergrads only just getting into Classics) that questions of antiquity ask things that we just don't know and are unlikely to be told. Strabo and Appian record Seleucus' peace with Sandracottus, but they do not tell us the details. Appian doesn't even mention the elephants at all, he just says something about a marriage contract, which Strabo echoes without elaborating at all. All Strabo has to say about elephants is that Seleucus was given 500 of them. That's it. Presumably there were some handlers and instruction or something, but we're not told that. We cannot know. All we know is that the rather implausible number of 500 elephants (which do not appear again in Strabo and do not correspond as far as I know to the forces at the Ipsus) was transferred, provided that we accept Strabo's testimony at all