The keypoolrefill RPC fills the keypool.
keypoolrefill ( newsize )
*bitcoin-cli help keypoolrefill
keypoolrefill ( newsize ) Fills the keypool. Requires wallet passphrase to be set with walletpassphrase call if wallet is encrypted. Arguments: 1. newsize (numeric, optional, default=1000, or as set by -keypool) The new keypool size Result: null (json null) Examples: > bitcoin-cli keypoolrefill > curl --user myusername --data-binary '{"jsonrpc": "1.0", "id": "curltest", "method": "keypoolrefill", "params": []}' -H 'content-type: text/plain;' http://127.0.0.1:8332/