'' I'm presenting and I want to change topic of the presentation for a moment and explain another topic , then come back to main topic ''
You could say:
"I'd like to put today's topic to one side for a moment (for a minute). I'll come back to it shortly (presently), but first I want to say a few words about ..."
"I hope you don't mind if I put today's topic to one side for a moment. I'll come back to it shortly, but first I'd like to say a few words about ..."
In this informal sense "minute" can, like "moment", mean a short period of time.
Of course, if the presentation is in the evening, then: "... this evening's topic ..."
Or more simply: "Before I get onto today's main topic, I'd like to briefly say a few words about ..."
not a teacher