Tax return after leaving France

I lived in France for six months in 2018 and registered as an auto-entrepreneur (opting for versement liberatoire). I left France in September 2018. I cancelled my auto-entrepreneur registration before leaving, but didn’t contact impots.

I have a few questions regarding my tax return for 2018:

1. Will I need to complete a tax return, seeing as I have already declared/paid tax on all my French income and have now left France?
2. If I do need to complete a return, could you let me know which forms I would need to complete (my only earnings during the period in France were as an auto-entrepreneur)
3. I gather the tax forms are usually sent out by post, but I don’t know if impots have my new address in the UK. Can the forms also be downloaded? (I have looked online for the forms, but they don’t seem to be available for 2018 yet). Alternatively, I could try to change my details with impots online, but it seems in order to set up an account as a particulier I need a numéro fiscal, which I don’t think I have because I haven’t declared tax in France before. Could you let me know whether this number should have been sent to me on any documentation?

Many thanks