Manual Method
Edit etc/sysctl.conf and append at the end:
net.core.default_qdisc=fq
net.ipv4.tcp_congestion_control=bbr
Run sysctl -p to save and apply
Automatic Method
echo -e "\nnet.core.default_qdisc=fq\nnet.ipv4.tcp_congestion_control=bbr" >> /etc/sysctl.conf && sysctl -p