Could someone please help me to understand the principle guiding the construction of this clause? Why is it not, „Wenn ihr wollt mehr wissen…“? I suspect it has something to do with this being a subordinate clause, or at least not the main clause, since the sense is incomplete. Is that right? The full sentence is, „Wenn ihr mehr wissen wollt, wie das geht, hier ist ein Video über Tickets in Berlin.“ Thanks.
Exactly. It's a dependent clause so it follows dependent clause word order.
You example is slightly incorrect though. There's a da-Adverb missing. Also, the word order in the concluding main clause is slightly off as well:
Wenn ihr mehr darüber wissen wollt, wie das geht, ist hier ein Video über Tickets in Berlin.
In German, let the position of the conjugated verb guide you. If it is near the end, that clause is a dependent clause. If it is near the beginning, it's a main clause.
So it's a second order dependent clause, then a first order dependent clause, and finally a main clause.