How can i generate a new random number after one round in c#?

I have a problem with my programm. I want to write a random number guessing game. I have actually everything but when i ask the user if he/she wants to do it again and he/she says yes, the same number from the 1. round is also in the second round. Like:

• Write your number down: 90.
• Great u guessed the number!
• Do u want to play again [y|n] y.
• write another Number: 90.
• Great u guessed the number!

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