1.You can try the advanced cycle feature.
Place the cursor on the frame where you want to insert the cycle.
Rightclick and choose Advanced Cycle. Decide first and last frame of the cycle bye draging the two sliders. Set a checkmark for forward reverse and Press OK. ( If you work on two’s, set Expose Each Drawing For to 2)
2.You can also select a range of frames in the timeline to copy/paste them.