1 – Backup
docker-compose exec mysql mysqldump -u root –password=xxx test > test.sql

2 – Get certificates
certbot-auto certonly –preferred-challenges dns –manual -d xxx.com -d *.xxx.com

3 – nginx changes

4 – Really Simple SSL plugin

5 – Swap and enjoy !

Edit – 02/03/2021
Because I am using Docker + Nginx + WordPress
Add in location of nginx conf :
proxy_set_header X-Forwarded-Proto $scheme;
https://serverfault.com/questions/659029/how-to-solve-nginx-reverse-proxy-mixed-contenthttp-https/853237
=> This removes the need for the Really Simple SSL plugin ! (Not free anymore)