Moving from EF db First to EF Core

Hi

I have a little app using EF db first and I want to move it to  EF Core.

I've used my models classes generated previously.but I got some errors:   

The entity type ... requires a key to be defined

or

SQL error Column unknown MYTABLEID 

 (I have MYTABLE and column ID  but not the table MYTABLEID )

What configurations should I have to do for EF Core because  my db provider doesn't yet support scaffolding.

thanks