Transformer design is very complex and I could not tell you how to do it. When I need a transformer, I either re-wind the secondary of an existing transformer, using the original primary, or contract for someone knowledgable to design it. I had a 4KW switching transformer designed and built for $100 US, which was a great bargain.
I suggest that you post the specifications here and see if there is a transformer designer who will respond. The designer will need to know:
The size, shape and material of the core.
the frequency
the output voltage and current
the input voltage
Good luck.