Check step by step procedure to enable POP in Gmail account setting.
Step 1: Open Gmail Account. In the top right corner, click on Gear icon and click Settings.
Step 2: Click on "Forwarding and POP/IMAP" option.
Step 3: In POP download section, click on radio button named Enable POP for all mails. Click on "Save Changes" button.
This action will enable POP for Gmail account.