You can do it through save editing and it isn't too complicated a process, but it can often leave some 'scars' in leftover bushes and terrain in weird locations, and is only possible on PC and mobile to begin with.
Otherwise I just recommend playing on with the save you have, it doesn't really make too large of a difference, and even if you don't want to entirely restart (very understandable), nothing's stopping you from just having two simultaneous files, one with forest farm and the other on beach farm