If you check the schedule in ExpertFlyer you can see those are the only days they are operating to ZRH that week. I don't know what day your original flight was scheduled, but it's seemingly been cancelled and there's no alternative.

RJ tends to be extremely insistent you use their metal and code on the segments touching AMM so I don't think you're going to get much more out of them without other viable alternatives available as LX also doesn't fly to AMM. In my experience RJ won't fully re-route you on other airlines without using at least some of their own flights, they'll just offer to cancel. Other accounts in this thread and in the premium fares forum support that as well.

You could try to get them to route you to somewhere else in Europe that RJ is actually flying on the day you need (or day before more likely), or get them to route you via CAI on RJ then MS / LX from there to ZRH. The closest point I can see a daily flight on RJ is FRA and some days to MXP.

I wouldn't count on the OTA to do anything, knowing how RJ tends to operate with cancelled flights, I think your options are quite limited and those would mostly likely force you to leave a day early.