How can i cure/aid forearm tendonitis?

Rest: It depends on which side of the arm. On the top (dorsal) stretch by bending the hand and wrist downwards and work on gentle wrist extension exercises with a very light wt like a can of soup. For the bottom (volar) do the exact opposite for stretching and strengthening. Don't forget nsaid's as well. Use ice initially, and then switch to warm moist heat after a few days if still symptomatic.