how do I turn off icloud back up and reminders on my mac book air

Hi tonyia24,

Welcome to the Apple Community,

where some of us do our best to help troubleshoot :)

Apple support have an article online: "Manage your iCloud storage"

Says:

To delete backups and turn off iCloud Backup

Mac

1. Go to Apple menu  > System Preferences > Apple ID, then click iCloud.
2. Click Manage and select Backups.
3. Select one of the device backups, then click — to delete. If you want to turn off Backup and remove all backups for that device from iCloud, choose Delete when you're asked to confirm.

When you delete a backup, it also turns off iCloud Backup for your device. You can turn iCloud Backup back on in iCloud settings on your device. 

Complete article: https://support.apple.com/en-us/HT204247

Also, for iCloud settings:

Set up your Apple ID iCloud settings on Mac

(NB choose your iOS at the top for accurate info:)

https://support.apple.com/en-au/guide/mac-help/mchlcfdfc3a5/mac

or

How to change your iCloud settings

https://support.apple.com/en-us/HT207689

Hope this helps you :-)