Jan, you could do two things.
One is send yourself an email with the instructions then Don't Deleted it. Subject Changing My Phone Time.
The other is to set two calendar entries, one in March and the other in October, repeating annually, with the same instructions.
The email one you will have to find. The Calendar one will pop up and remind you twice a year with the instructions and it will be on the same month as your time change so easy to find.
I forgot. I only need to change the watch as it is the only thing I carry around that does not change the time automatically. I was on the train to Gatwick when I realised. I changed the clock on the bike when I was sitting in traffic. After finally getting the bike started with the help of not one but two lithium ion jump starters. It's been sitting at Gatwick airport for 7 months and the brakes were a bit stiff too.