The question is how you know it is wrongly wired? It is unlikely that swapped line and neutral would cause a RCD to trip. But if line is connected through a fault to earth on a TT installation it could bring the protective equipotential bonding up to line voltage and show as reverse connected on simple plug in testing devices.
This would be very dangerous as anyone touching metal on your house i.e. drain pipe and similar on neighbours house could get lethal shock.
What size is RCD i.e. 30ma or 100ma and what type of earth is used in house TN-C-S (PME) or TT (Earth Rod).
I would recommend you call an electrician ASAP I hope I am wrong but better to be safe than sorry.
A straight answer to your question on reverse polarity.
socket in kitchen supplying toaster, 90% of socket outlets are only single pole switched ie only break the connection to the pin which should be live.
If socket wired wrong polarity when switched 'off' at outlet the toaster would cease to work due to loss of neutral HOWEVER when you stick the metal knife in to remove the stuck bit of toast it's still live between element amd metal case of toaster you are holding!!!
It's you that will be 'Brown-Bread'!!
As ERIC says this is unlikely to be cause of tripping RCD, but should be corrected anyway.
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