Hello dear Apple group ,well iCloud shows me that I have 418MB of content in there but I don’t have that much content in my message , I don’t know how can I delete all those 418MB Of content from

Hi mohammadzohouri

welcome to the Apple (user-to-user) Community.

Re: I don’t know how can I delete all those 418MB Of content from

418MB is less than half a GB / not such a huge amount. (Some could be photos etc.)

You can delete messages from your iPhone to delete synced content from iCloud.

(or you could see if you can just delete images, emoji, photos, videos, audio, etc)

Eg: How to: Manage your iCloud storage – Apple Support

says:

"Delete a message or attachment on your iPhone or iPad

In a message conversation, touch and hold the message bubble or attachment that you want to delete.

Tap More.

Tap Delete , then tap Delete Message.

If you want to delete all messages in the thread tap Delete All, in the upper-left corner. Then tap Delete Conversation.

Delete multiple attachments from a contact or conversation

In a message conversation, tap the contact's name at the top of the screen.

Tap Info 

In the Photos section, tap See All. 

Tap Select, and tap the images you'd like to delete.

Tap Delete, then tap Delete Attachment to confirm. 

Delete an entire conversation 

Swipe left over the conversation that you want to delete.

Tap Delete.

Tap Delete again to confirm. "

All the best :-)