Yes, I found it! I created an input, then in the card inside botpress studio I passed the variable

{{event.conversationId}}

, in my action I receive the input and retrieve the tag like this:

ts
 if (!input?.conversationId) { return { ok: false } }
 const { conversation } = await client.getConversation({
   id: input.conversationId
 });

 if (!conversation || !conversation?.tags['mysystem:id']) { return { ok: false } }

 const letsGoMyVariableInConversationTag = conversation?.tags['mysystem:id'];