You could, ah, change the management at La Vents.
Rather stupidly, before investigating how come La Venta "owned a settler already" ... I invested time and effort into becoming suzerain of both. It could still be done, because La Venta would join my war against Chinguetta and (presumably!) capture that settler, then I could attack La Venta and get it back .. but this far into the game I think I would lose more by burning all my envoys, then a new settler is worth.
I suppose once I get the tech, i could open the tunnel for them to get out and settle somewhere, but there might not be anywhere left by then!Would be fun to mountain tunnel into it late for a free settler. Although especially as Portugal, Chinguetti is more valuable alive than as a new city I think, so I would just enjoy there never being any competition for it unless if someone else takes control of La Venta.