Hello again! It depends if you're using "swing" as a verb or as a noun. If it's the former, you would say "columpiarse" or "balancearse". Be aware that this is a "self fulfilling action" in Castillian, so you would have to conjugate it with the pronouns (yo me columpio/ balanceo, tu te columpias/balanceas, el se columpia/ balancea...). If the action is made by you to another person you wouldn't need the pronouns (yo columpio a..., tu columpias a..., él columpia a...).
If you mean "swing" as a noun (where the children play in a park) it would be "columpio". Hope this helps!