i lost my iphone backup in finder app in my macbook how can find it??? very important for me this backup

Backups are stored at

~/Library/Application Support/MobileSync/Backup/

Refer to "Find backups stored on your Mac or PC" in Locate backups of your iPhone, iPad, and iPod touch - Apple Support.

If the backup is not found at that location, then it was either never created to begin with, or it has been deleted.

Backups are overwritten and never deleted automatically; you have to do that on your own. If you deleted the backup and you backed up your Mac with Time Machine, then navigate to that folder and "Enter Time Machine". Refer to Restore items backed up with Time Machine on Mac - Apple Support.

Do you still have your iPhone? If the backup file is gone for whatever reason, you still have your phone, I assume, and can create another backup any time you wish.