Hello!
Year 13 student here. Its great to hear you're looking for work experience for your plan to become an optician.
My first thought is it can be tricky to find the 'ideal' work experience, such as working with an actual optician, I recommend finding work experience first by contacting opticians stores, like Specsavers and Boots, use both digital (email) and even physical (asking in person) forms of communication to find some work experience. You may be able to help staff out front whilst building valuable skills like customer service and team work, additionally you'll get a feel for what its like to work in an optician's workplace.
You can also just focus on any events that foster the skills associated with being an optician (e.g organisation, patience, customer service, communication), maybe finding a part-time job in hospitality would be a good experience to mention in a personal statement (assuming you're going on to A-Levels). Alternatively, volunteer work at charity shops are always a great way to harbour valuable skills when it comes to your career aspirations.
Overall, work experience can be found by contacting optician stores near you or even further if say, your local stores don't respond or offer work experience. There are also many other 'indirect' ways of developing your skills that would make you a suitable candidate for a course to become an optician, like as mentioned a part-time job or volunteer work.
I hope you find what helps you in your journey to become an optician, just don't give up finding experience!