While I try to download any app from App Store, it shows , you cannot login because your account has been locked’ . How can I fix this problem?

There is some sort of funding problem in your account; you must contact a live person at iTunes store support to resolve it. There is a link in this article to do just that→If you see a message that says 'Your account has been disabled in the App Store and iTunes' - Apple Support

See the instructions in here.

If your Apple ID has been locked or disabled – Apple Support

Follow the steps in the Related Article you linked to the forum with. You need to contact Apple Support.