If you start again from block zero your it is not a fork, but a new blockchain from the scratch.
“Fork” means that if the current blockchain is at block N at the fork instant, the forked blockchain shall be identical up to block N, free to be different from block N+1.
For your aim it should be enough to choose the parameters for the genesis block (i.e. block zero) and to start the blockchain.
Make a simple research to define the few parameters value to write in block zero you need. The true Ethereum block zero (that from the current chain) described a blockchain parameters set different from that today in use (you need to understand what you exactly need for your application).