In SharePoint Admin Center you have to enable "Custom Script" options to "Allow". After this change, system will take around 24 hours to affect the site collection settings. Then that JS Link option will show-up.
Allow users to run custom script on personal sites
Allow users to run custom script on self-service created sites
O365 Admin--> SharePoint --> Settings
If you want it to be run right away after these settings than use below mentioned PwoerShell commands:
Connect-SPOService -Url https://sitename-admin.sharepoint.com/ -credential email@example.com
Set-SPOSite -Identity https://sitename.sharepoint.com/ -DenyAddAndCustomizePages $false
echo "Successfully completed."
in addition, you can also Use SharePoint Designer for changing JSLink. Open your list in SharePoint Designer, then click to the view, and in the page editor you should be able to find the JSLink tag. Change its contents and that's it.
Where is the "JS Link" property?