The card game Kaschlan appears to share similarities with the Russian card game Durak. In Durak, the rules to determine how a new attacker is chosen are as follows:
For more detailed rules on Durak, you can refer to sources such as the Wikipedia page on Durak here.
If Kaschlan's rules are slightly different, it might be necessary to look up specific rules of this game, but often traditional card games share these common principles for switching roles between players.