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Something like this might help
https://www.ebay.co.uk/itm/295540959036
And a mini trimmer like this that you can hold with two fingers close to the clipper head will be easier than using a the bulkier clipper that you would use for the rest especially if it has a cable
https://www.lookfantastic.com/wahl-pocket-pro-battery-trimmer-black-rubberised/10785409.html
For doing the sides of the hairline you should be able to turn your head to the side as see the neckline so hold the trimmer vertical and just go straight down ear to neck
Does anyone have any tutorial video recommendations.
I've been cutting my own hair for >20 years, but I still manage to make a mess of my neckline occasionally - It's probably about time I figured out how to avoid looking like I've just escaped from an institution.