To migrate an existing PostgreSQL database to DigitalOcean, you will need to do the following:

1. Sign up for a DigitalOcean account and enable the Managed Databases for PostgreSQL service.

2. Create a new PostgreSQL database on DigitalOcean using the DigitalOcean Control Panel, the doctl command-line tool, or the DigitalOcean API.

3. Export the data from your existing PostgreSQL database using the pg_dump utility or a similar tool.

4. Import the data from the dump file into your DigitalOcean PostgreSQL database using the psql utility or a similar tool.

5. Verify that the data has been imported successfully and that your DigitalOcean PostgreSQL database is working as expected.

Once you have completed these steps, your existing PostgreSQL database should have been migrated to DigitalOcean and be fully operational on the DigitalOcean Managed Databases for PostgreSQL service. You can then continue to use the standard PostgreSQL tools and APIs to manage and query your migrated database on DigitalOcean.

It is recommended that you test the migration process and verify the data in your DigitalOcean PostgreSQL database before switching over to using it in production. This will ensure that the migration process was successful and that your DigitalOcean PostgreSQL database is functioning as expected.