Hey PJV, If you were certain what paint you used you could try the thinners that are specific to the paints but I think it would be a long job. However the easiest way is to use some acetone or some 2k thinners, that stuff doesn't care what paint you've used and I have used both in the past when i've left paint in the cup for a while or when I've brought a 2nd hand airbrush off eBay. As per usual, if you want to soak the front end make sure you remove any seals if you can, you can drop some in the cup and leave it for a while, use a semi firm brush or an old tooth brush to clean in the cup. Wash out with water afterwards. You will probably have to do it a few times. when you think its clean enough try shooting some thinners or acetone through the airbrush, be aware you should mask up for that bit or aim it outside.
Sorry to hear you've been ill, but happy your well enough to start again and be able to come home to the forum, we got your back here.
lee