Unscrew these yellow marked screws, then take the cover off. Same on the top. Gives you only access to the bottom of the toerail.
The entire back panel will not come off without taking the entire starboard furniture apart, which is probably not possible in a non-destructive way because a) the furniture was fitting from the top before the deck came on and b) the screws were not stainless and will have corroded into the wood and snap off when you try.
If you do need the full panel off for some reason, then tape up the edges and cut with an oscillating multitool sawblade along the edges. You can then later attach some spacers to the hull and fit the back panel onto those to look more or less the same. The only reason I can think of for doing this would be severe hull damage though?
