Con Ed Red Tag: Plumber Recommendation

One of our tenants called Con Ed and reported they smelled gas in their apartment when they couldn’t reach the super. Con Ed came and locked down their gas meter and put a “red tag” on it. Super informs us this happened last spring when their pilot light had blown out with open windows and he just relit the pilot! We’re told we need to hire a licensed plumber to test (and fix if needed) the gas line. A couple of questions… How does the plumber test the line when the meter is locked? Do they have keys for those locks? What if any permits are required and what is a fair price for the job (not including any re-piping that probably won’t be necessary)? Finally, can anyone recommend a reasonable plumber to do this? Thanks.