First, you should see if you can access your policy online. Hopefully, you already have an account set up, but you can create one using some basic information if you do not. Once logged in, you can access your documents and manually make any changes to your policy there.
If you cannot log in online, or your car insurance company does not offer this feature, the next thing you should do is give them a call. After explaining the situation (I guarantee you’re not the first to misplace policy documents), they will likely send replacement documents to your email or physical address.