1. Get the output from Ambari server
2. Copy the json of "operating_systems" outer block of step1 output and create repo.json file -
it would looks like repo.json
3. update repo.json file to reflect your changes/modifications.
4. now run below API call to update.
curl -insecure -H "X-Requested-By:ambari" --user admin:admin --data @repo.json -X PUT http://AMBARI-HOST:8080/api/v1/stacks/HDP/versions/3.1/repository_versions/1
Note: please make sure you include correct repo version id at the end. in this case it is 1
5. Now go and check in UI to see if those changes reflects.
Note: This tried and tested in Ambari2.7.x
Helpfull Article to update Repo URLS incase manage version UI is not loading.