2 John 1:4 I rejoiced greatly that I have found some of your children walking in truth, as we received commandment from the Father. 5 And now I plead with you, lady, not as though I wrote a new commandment to you, but that which we have had from the beginning: that we love one another. 6 This is love, that we walk according to His commandments. This is the commandment, that as you have heard from the beginning, you should walk in it.

From https://gotquestions.org/elect-lady-2-John.html

John calls the lady in 2 John “the elect” because she believed in Jesus Christ and was therefore saved; she was a member of the universal Church. Some interpreters see the lady not as an individual but as a symbol of the church as a whole or of a local body of believers. But that interpretation makes it difficult to explain who her “children” are. It is better to view this lady as an unnamed friend of John who had actual children who were serving the Lord.

It is not a new commandment, it is an old one: Love one another. We are to love one another and walk according to His commandments as we have heard from the beginning.