code: public function changeConnectionName($connection)
      {
          if (!array_key_exists($connection, $this->connectionList)) $connection = '';
  
          $resolvedConnection = $this->manager->getResolvedConnectionName($connection);
          if ($resolvedConnection != $this->getConnectionName()) {
              // changed
              // save the new connection to be used as default for the user
              try {
                  $this->manager->setConnectionName($resolvedConnection);
                  $this->loadPersistentData();
                  Cookie::queue($this->cookieName(self::COOKIE_CONNECTION_NAME), $connection, 60 * 24 * 365 * 1);
              } catch (\Exception $e) {
                  Cookie::queue($this->cookieName(self::COOKIE_CONNECTION_NAME), '', 60 * 24 * 365 * 1);
  
                  if (!$this->manager->isDefaultTranslationConnection($resolvedConnection)) {
                      // reset to default connection
                      $this->manager->setConnectionName('');
                      $this->loadPersistentData();
                  } else {
                      // invalid database config or no connection
                  }
              }
          } else {
              Cookie::queue($this->cookieName(self::COOKIE_CONNECTION_NAME), $connection, 60 * 24 * 365 * 1);
              if (!$this->transLocales) {
                  $this->loadPersistentData();
              }
          }
      }
docs: Change default connection used for this login/session and reload
  persistent data if it the connection is different from what was before
  
  @param $connection string    connection name to change to