Now you need create a custom field for issues, follow steps:
1) Go to Settings → issues
2) Go to Custom field → click on create custom field
3) Find MLCS (Advanced → Multi Level Cascading)
4) Set a name
5) Select all screens and context where you need custom field
6) MLCS now are available on any issue
1) Click on the three dots, then select "Contexts and Default Value."
2) Click "Edit Custom Field Configuration."
3)You can now add the field configuration and click Save