If you have created the migrations, you could execute them in the Startup.cs as follows.

public void Configure(IApplicationBuilder app, IHostingEnvironment env, ILoggerFactory loggerFactory)
 {
      using (var serviceScope = app.ApplicationServices.GetService<IServiceScopeFactory>().CreateScope())
      {
            var context = serviceScope.ServiceProvider.GetRequiredService<ApplicationDbContext>();
            context.Database.Migrate();
      }

      ...

This will create the database and the tables using your added migrations.

If your not using Entity Framework Migrations, and instead just need your DbContext model created exactly as it is in your context class at first run, then you can use:

public void Configure(IApplicationBuilder app, IHostingEnvironment env, ILoggerFactory loggerFactory)
 {
      using (var serviceScope = app.ApplicationServices.GetService<IServiceScopeFactory>().CreateScope())
      {
            var context = serviceScope.ServiceProvider.GetRequiredService<ApplicationDbContext>();
            context.Database.EnsureCreated();
      }

      ...

Instead.

If you need to delete your database prior to making sure it's created, call:

context.Database.EnsureDeleted();

Just before you call EnsureCreated()

Adapted from: http://docs.identityserver.io/en/latest/quickstarts/7_entity_framework.html?highlight=entity