Sorry about the trouble with Lightroom mobile. We're here to help.
Would you mind sharing the version of Lightroom mobile you're working on along with the version of Android you're running on the device? Are you getting an error while trying to delete the images?
You may want to delete all the images. You can also try going to Preferences > Lightroom Mobile, there's a Delete All Data button.
If you're using the app through a subscription, please try going to Lightroom.adobe.com & check if you're able to delete the images from there. You can also try re-installing the app to check if that helps.
Note: If you're using the free version of Lightroom mobile, please do not re-install the app.