dont know of any apps or websites but I also struggled to find work experience last year. I would recommend emailing local (in your city) smaller businesses or calling them. do a bit of research in the company to show that you have a passion for work experience there and any work experience is good (especially if you dont have a part time job) even if its not in the sector youre looking for. some unis also offer work experience type of things so try emailing any unis near you aswell. What kind of work experience are you applying for?