You need to work out exactly which Mira model you have. Once you've done that, head to https://www.showerdoc.com/shower-spares/mira
Find your model and scroll down the page. You should find plenty of FAQs there. If your own symptoms aren't mentioned you can ask for your own problem.
howtomendit.com for free repair help, information and advice.
Try fixfault.com to fix baths and showers.