Can you give 12.3 Volts on Vin pin of Uno?

[PaulRB]

@umersalam123-456

Any recommendations that you could give?

You could use a DC-DC voltage converter, otherwise known as a "buck regulator". There are lots available on eBay etc. Choose one with significantly more current capacity than you need.

@umersalam123-456

And it would be great if you could explain if the current being drawn in any circuit has an effect on the resistors? I am a newbie and this resistor thing really confuses me.

You need to study the law.