Please have a look at the certbot-dns-digitalocean documentation first.

Procedure :

• Edit domains in the compose file
• Edit DigitalOcean credentials in digitalocean.ini file (generate using https://cloud.digitalocean.com/settings/api/tokens)
• Run certbot only and wait for certificates to be generated : docker-compose up -d mycertbot
• When certificates are generated, run your services : docker-compose up -d