Here goes! (US ALSO Here goes nothing!) INFORMAL
said just before you do something brave or something that you have never done before:
Well, I've never ridden a motorbike before, so here goes!

[TahlilGaran] Advanced Learner's Dictionary ▲

here goes
I will now do this.
I owe you an apology and an explanation, so here goes.

[TahlilGaran] English Idioms Dictionary ▲

Here goes.
ready to to do something while hoping for the best results
"Well, here goes. I am going to go and ask that girl for a date right now."

[TahlilGaran] English Idioms Dictionary ▲

here goes
interj., informal I am ready to begin; I am now ready and willing to take the chance; I am hoping for the best.
■ Said especially before beginning something that takes skill, luck, or courage.
"Here goes!" said Charley, as he jumped off the high diving board.
"Here goes!" said Mary as she started the test.

[TahlilGaran] English Idioms Dictionary ▲