See this page for more details about the Collections API:
https://lucene.apache.org/solr/guide/8_5/collections-api.html

• HTTP Request (URL):
  http://localhost:8983/solr/admin/collections?action=CREATEALIAS&name=collection_1_2_alias&collections=collection1,collection2
  
  
• Java sample:
  private void createAlias(final int jettyPort, final String aliasName, final String aliasedCollections) throws IOException { final String url = "http://localhost:" + jettyPort + "/solr/admin/collections?action=CREATEALIAS" + "&name=" + aliasName + "&collections=" + aliasedCollections; final HttpGet request = new HttpGet(url); try (final CloseableHttpClient client = HttpClientBuilder.create().build(); final CloseableHttpResponse response = client.execute(request)) { final HttpEntity entity = response.getEntity(); System.out.println(IOUtils.toString(entity.getContent(), "UTF-8")); // close the content stream. EntityUtils.consumeQuietly(entity); } }

• HTTP Request (URL):
  http://localhost:8983/solr/admin/collections?action=DELETEALIAS&name=collection_1_2_alias
  
  
• Java sample:
  private void deleteAlias(final int jettyPort, final String aliasName) throws IOException { final String url = "http://localhost:" + jettyPort + "/solr/admin/collections?action=DELETEALIAS" + "&name=" + aliasName; final HttpGet request = new HttpGet(url); try (final CloseableHttpClient client = HttpClientBuilder.create().build(); final CloseableHttpResponse response = client.execute(request)) { final HttpEntity entity = response.getEntity(); System.out.println(IOUtils.toString(entity.getContent(), "UTF-8")); // close the content stream. EntityUtils.consumeQuietly(entity); } }