Apologies if you've already tried this or something similar, it doesn't work for everyone, but I got mine back by using essential oils to retrain [edited as my phone autocorrected to 'restrain'] my olfactory system. After over a year of my food tasting like trash, or like it was off, and a dangerous incident (with a trip to A&E) where my brain fog meant I left an unlit gas oven on all night and couldn't smell it until I'd already got carbon monoxide poisoning (thankfully mild and temporary), I regained my smell and taste in about a week. Here's an article about it, it links to a charity that works in the field of loss of smell : https://www.saga.co.uk/magazine/health-wellbeing/treatments/smell-training-for-anosmia

Edit: if the down votes are because people think this is alternative medicine or woo, it isn't, it's a technique used in conventional medicine clinics. Try reading before you down vote.