It depends on the operating system. Shut down your node. If you are running any Linux distribution then add "-fallbackfee=0.00001" to the launch command e.g. "bitcoind -fallbackfee=0.00001". If you are running Windows then right-click on the Bitcoin Core executable file, select Properties and add "-fallbackfee=0.00001" after the file extension. The fallback fee will be set to 1 sat/byte which should be enough for now. By default, it's 20 sat/byte if you don't specify the value.