CloudVeil Messenger (CVM) is a modified version of Telegram. Questions about basic Telegram features—like creating polls, managing groups, changing notification settings, archiving or unarchiving chats, or deleting messages—are answered in Telegram's official documentation.
Since these are Telegram features (not CVM-specific), you'll find answers in Telegram's official documentation. Telegram's Frequently Asked Questions and how-to guides are available at https://telegram.org/faq. You can also search the web for Telegram tutorials that apply to your question.