Good morning, @Bhaktkd ...
Based on your question, it sounds like your students are seeing a padlock icon on your course "Modules" page similar to what is described in this Student Guide: How do I view Modules as a student? - Canvas Community. If this is the case, you may need to look at your course Prerequisites and/or Requirements that may be configured for one or more modules in your course. Here are a couple Guides for you:
I hope these resources will be of help to you. Sing out if you have any other questions about this...thanks! Take care, stay safe, and be well.