Tell him you already opened it, but he can have the letters back

From Create Your Own Story

You gesture to Raquel to bundle up the letters. "We already opened the chest!" you yell to the other captain. "What gold and silver there was we're keeping. But I believe you want your letters back?"

"Yes, I do!" he shouts as the ships draw closer. "So either give them back or we'll take them by force!"

You pull the Midnight alongside the galleon. "They are useless to me," you say. "What am I going to do with old love letters? My crew are interested in gold, not romantic musings." You take the letters from Raquel and indicate to the other captain to reach across the gap between your ships. He does so and you hand him the bundle of love letters.

"Good choice, Captain," the other captain says. "Now begone while I'm still in a good mood."

You direct your ship away from the galleon and gather your crew together.

Hang around the Rio Amarillo a bit longer, looking for more ships to ambush

Head at top speed for the stronghold of Majelca to find that treasure!