Alright. You should go step by step like, First you do code for displaying some characters on the LCD, later a string. Then try code for transmitting and receiving serial data. If you do all these yourself, you’ll find it very easy to code your project.
All you have to do is to keep the default or predefined UID in a string, store the serially received UID in another string and compare both of them using strcmp or strncmp. Display your message based on whether the strings match or not.
I hope you try out yourself, and if you stuck somewhere simply update on this forum. You will defenitely get help.