dotnet core - Entity Framework - problems with creation of migration - cant find SDK

I have the latest Visual Studio 2019 preview 3.1.200-preview-014883.

I am trying to run the creation of a migration using this:

dotnet ef migrations add INITIAL --context CATALOGContext -s ../Jobsledger.API

but am getting the message:

Install the [3.1.200] .NET Core SDK or update [C:\Users\simon\OneDrive\Documents\1.0 - AURELIA\1.0 - JobsLedgerSPA -ASPNET CORE 3.1\JobsLedger.CATALOG\global.json] with an installed .NET Core SDK:
  3.1.101 [C:\Program Files\dotnet\sdk]
  3.1.200-preview-014883 [C:\Program Files\dotnet\sdk]

I've upgraded Visual Studio - and updated global.json with the following:

{
    "sdk": {
        "version": "3.1.200"
    }
}

How do I run the migration - what am I missing here as I thought I had the SDK installed with the preview?

UPDATE: I ran the following

dotnet tool install --global dotnet-ef --version 3.0.0 

and got the following:

Install the [3.1.200] .NET Core SDK or update [C:\Users\simon\OneDrive\Documents\1.0 - AURELIA\1.0 - JobsLedgerSPA -ASPNET CORE 3.1\JobsLedger.CATALOG\global.json] with an installed .NET Core SDK:
  3.1.101 [C:\Program Files\dotnet\sdk]
  3.1.200-preview-014883 [C:\Program Files\dotnet\sdk]
PS C:\Users\simon\OneDrive\Documents\1.0 - AURELIA\1.0 - JobsLedgerSPA -ASPNET CORE 3.1\JobsLedger.CATALOG>  

I also ran

dotnet tool install --global dotnet-ef --version 3.0.2

and got the same as above..