In Salesforce there are two methods to set password and to reset password for a user.

resetPassword(Id userId, Boolean sendUserEmail): This method resets the password for the specified user. When the user logs in with the new password, they are prompted to enter a new password, and to select a security question and answer if they haven’t already. If you specify true for sendUserEmail, the user is sent an email notifying them that their password was reset. A link to sign onto Salesforce using the new password is included in the email.

setPassword(Id userId, String password): Sets the password for the specified user. When the user logs in with this password, they are not prompted to create a new password.

Sample Code:

List<User> users = new List<User>();
String username = 'test@test.com';
users = Database.Query('SELECT Id, Name FROM User WHERE UserName  =: username');

for(User u : users){
    //For reset User password
    System.resetPassword(u.Id, true);
    
    //For set User password
    //System.setPassword(u.Id, 'Test@1234');
}