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