+1 to much of the advice, but especially the last two.
Find a big empty area that you can use on your own for a while, then get out there for 10-15 minutes every evening for a week. Start off just swinging the bike around in large circles / figure-8s with both hands on the bars, then try and lift your left hand an inch off the bars and repeat the shapes until your feel more confident, then with the right hand an inch above the bars and repeat, and gradually move your hand further away until you can get your arm out completely.
But, remember that "indicating" means you are "indicating to other road users that you are
about to change direction and / or speed". Indicate in advance of the manoeuvre and get both hands back on the bars to perform the manoeuvre.
IMO, of course.
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