Install rails_admin and devise. Start setting it up.

db/migrate/20200817200957_devise_create_admins.rb

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+# frozen_string_literal: true
+
+class DeviseCreateAdmins < ActiveRecord::Migration[6.0]
+  def change
+    create_table :admins do |t|
+      ## Database authenticatable
+      t.string :email,              null: false, default: ""
+      t.string :encrypted_password, null: false, default: ""
+
+      ## Recoverable
+      t.string   :reset_password_token
+      t.datetime :reset_password_sent_at
+
+      ## Rememberable
+      t.datetime :remember_created_at
+
+      ## Trackable
+      # t.integer  :sign_in_count, default: 0, null: false
+      # t.datetime :current_sign_in_at
+      # t.datetime :last_sign_in_at
+      # t.inet     :current_sign_in_ip
+      # t.inet     :last_sign_in_ip
+
+      ## Confirmable
+      # t.string   :confirmation_token
+      # t.datetime :confirmed_at
+      # t.datetime :confirmation_sent_at
+      # t.string   :unconfirmed_email # Only if using reconfirmable
+
+      ## Lockable
+      # t.integer  :failed_attempts, default: 0, null: false # Only if lock strategy is :failed_attempts
+      # t.string   :unlock_token # Only if unlock strategy is :email or :both
+      # t.datetime :locked_at
+
+
+      t.timestamps null: false
+    end
+
+    add_index :admins, :email,                unique: true
+    add_index :admins, :reset_password_token, unique: true
+    # add_index :admins, :confirmation_token,   unique: true
+    # add_index :admins, :unlock_token,         unique: true
+  end
+end