The clearbanned RPC clears all banned IPs.
clearbanned none
*bitcoin-cli help clearbanned
clearbanned Clear all banned IPs. Examples: > bitcoin-cli clearbanned > curl --user myusername --data-binary '{"jsonrpc": "1.0", "id":"curltest", "method": "clearbanned", "params": [] }' -H 'content-type: text/plain;' http://127.0.0.1:8332/