Not possible to answer the question without sctually being on the job.
It wouldnt be adviseable to forcefully pull the pipes through, too much risk of damaging electric cables, other pipework such as water feeds to the radiators etc.
You definitely need to speak to the gas fitter TODAY to pre warn him. It isnt fair not too, both for the covid issue and the loss of earnings for the time he has set aside to do the job. If not he may bill you for his time especially if he cannot do it.

Hi mich,

It sounds like you will have to wait for access to the room. Not only will it depend on how the gas supply is run, but the engineer will also need to disconnect it from the tenants room before he could even try to attempt to pull the gas through.

Hi mich,
I'm afraid this would not be possible. You would have visually assess the route of the pipework to ensure it isnt connected anywhere and that it wont get caught or snag any other services (cables or pipe etc) or any other obstructions. Sorry.

No don’t do it if all appliances are operating especially in Covid times why do it in other times