How can I connect my Karaoke Condenser USB microphone to my amplifier?

Answer 1

The microphone needs to be powered and it needs an adapter that fits the amp's input.

Answer 2

Short version: You don't.

Get an inexpensive ($20 to $50) dynamic mic,
such as a Shure PG48 or Audio-Technica Pro 31QTR,
which doesn't need any power
and will work with any normal amplifier that has a mic input.

Answer 3

USB devices like that can only connect to computers, sorry...
[Or computer-based devices].

USB is a digital master-slave system; a mouse, keyboard, microphone etc. is a slave device and needs an "intelligent" system (the master) with the correct drivers to work out exactly what is connected and how to communicate with that device.

If you want a cheap-and-cheerful mic that will connect directly to an XLR with phantom power, look at the NW/BM 700/800 types that are available from many places.
You can get one of those for 10- to 15- eg. on ebay.

As with almost all mics advertised as "condenser" and pushed at non technical users, they are simply electret capsules in big casings - likely the same as applies to your karaoke mic.
At least they are cheap; some at 200- to 300- use the same scam description.

If you want a real condenser mic, the cheapest ones I know of are the MXL V67g or MXL 990, both of which are excellent value.

Examples - NW700:
https://www.ebay.co.uk/itm/Neewer-NW-700...

Note that you need an XLR to XLR cable to go with this (or the ones below). The XLR to mini jack cables with those fake condenser mics do nothing useful and should be thrown away.

MXL V67G
https://www.ebay.co.uk/itm/MXL-V67G-Larg...

MXL 990
https://www.ebay.co.uk/itm/MXL-990-Large...