CHANGE ODK AGGREGATE Server 2.0 URL

1. What is the problem? Be very detailed.
I have existing ODK Aggregate Server 2.0 under Digital Ocean with a URL based on freedns.afraid.org (per suggestion in the instructions from installation guide from opendatakit.org). It has been running for several months already, able to connect the ODK Collect and upload data to ODK Aggregate Server. Also have extracted data from the ODK Aggregate server.

Only at last week of September, the url was not accessible any longer. I have decided to purchase a domain name to replace the one from freedns.afraid.org. I have already updated the digital ocean's settings and am now able to access the ODK Aggegate server using the new url.

Meanwhile, I have updated the ODK Collect server details using the new url. However, ODK Collect is not able to download forms from the ODK Aggregate server. The error message says: Unable to resolve host (old url): No address associated with hostname Copying media files failed.

ODK Collect is not able to upload/submit data. The message says: Unexpected redirection attempt to an different host: https://(old url).

Please advise how to change the url to the new domain name in the aggregate server.

2. What app or server are you using and on what device and operating system? Include version numbers.

Server is from digital ocean.

3. What you have you tried to fix the problem?

4. What steps can we take to reproduce the problem?

5. Anything else we should know or have? If you have a test form or screenshots or logs, attach below.