Hey Goughy75,
I recently started doing the maintenance on my e-mtb myself. At first it seem quite scary, but luckely there's alot of youtube movies on how to do it! And once you know how to do it, it will be easy. Not to mention the money you save along with the pround feeling of having done it yourself! And you can do it at home vs leaving your bike for a few days at the bike shop.
I personally own a rockshox fork, but the steps are about the same. Here's a few video's on it for your fork:
SRsuntour Aion fork service
Sr Suntour Aion 35 mtb fork
Here's a link to the Suntour technical video section
Video section
You will need some basic tools (allen keys, mallet, syringe, degreaser/alcohol, 10mm wrench) a bike mechanic stand does really help
Things you'll need to buy:
*Suntour 35mm oil ring
Shop link
*80w oil (this is the specification i could find on the internet. This type of oil in not really mainstream fork oil.. i'm not 100% sure, but i think they mean the type of oil in this link
Oil link) It does need to be synthetic oil.
*fork grease (Rockshox uses sram butter.. i don't know if suntour requires special grease)
Shop link
*Suntour 35mm stanchion wiper seal (the old ones are probably still ok and just need some TLC)
Shop link
I don't know any bikeshops in the UK, but its worth looking arround for good prices. Make sure you get the correct oil rings (35MM). And if you plan on doing the maintenance youself in the future, maybe buy some oil rings in bulk to get a better price.