The dumpprivkey RPC reveals the private key corresponding to 'address'.
dumpprivkey "address"
*bitcoin-cli help dumpprivkey
dumpprivkey "address"
Reveals the private key corresponding to 'address'.
Then the importprivkey can be used with this output
Arguments:
1. address (string, required) The bitcoin address for the private key
Result:
"str" (string) The private key
Examples:
> bitcoin-cli dumpprivkey "myaddress"
> bitcoin-cli importprivkey "mykey"
> curl --user myusername --data-binary '{"jsonrpc": "1.0", "id": "curltest", "method": "dumpprivkey", "params": ["myaddress"]}' -H 'content-type: text/plain;' http://127.0.0.1:8332/