The field on the alm_asset table labeled Configuration Item for some reason is named 'ci', so this part of your script would be

else if (current.variables.pr_number) { current.configuration_item = current.variables.pr_number.ci; // Map pr_number to configuration_item }

Also, for some reason there are two fields labeled 'Configuration item' on the sc_req_item table, one named 'cmdb_ci' and the other named 'configuration_item' so ensure you are setting the correct one in your script for your environment based on the field that is shown on the form...