Clear userform if expiry date exceeds Today

Hi, attached is a file that we use to generate labels for our reagents. After selecting a reagent and the lot number, an expiry date is populated based on the data in the "Expiry" tab. What I hope to achieve is to have a popup msg appear when a user selects an expired chemical and the userform will clear so that the user can start again. Have tried some methods including addition of a textbox that shows today's date, but seems like im not getting it right.The textbox showing today's date can be removed if it is not required.