initial condition > if you are doing steady state, does not matter, it is just a starting point, but if you choose it close to the final answer, your solution will converge
wall condition > if you can assume the soil stays at the same temp all the time, apply 35deg C. if you model the soil, apply whatever the BC is that you know. for example if this is underground, maybe at the ground, it is a heat transfer condition, and underground a temperature.
i'd recommend checking out the tutorials to get started. the cross flow heat exchanger will point you in the right direction