This code assigns role to a list of users separated by new line, but only users in cache. How can I implement message.guild.members.fetch() to this code to assign role to all users?

//command
!roleAssign @role
name#1234
name#2234
name#3234

const roleAssign = function(message){
  const Role = message.mentions.roles.first();
  // split by new line
  const users = message.content.slice(prefix.length).split(/\r?\n/).slice(1);
  const success = [];

  users.forEach(user => {
    const u = client.users.cache.find(u => u.tag === user);
    if(u){
      const userId = u.id;
      // person with the userID
      let person = message.guild.members.cache.get(userId);
      // give role to person

      try{
        person.roles.add(Role)
      }
      catch(e){console.error(e)};

      if(person.roles.cache.has(Role.id)){
        success.push(user);
      }
      }
  });

  message.channel.send(`Added role ${Role.name} to\n${success.map(user => user).join("\n")}`);
}

I tried this but got TypeError: Cannot read properties of undefined (reading 'find')

message.guild.members.fetch().then((members)=>{
  message.cache.find(u => u.tag === user);
})