Dropdown selection appending

I have a question regarding dropdown selection updating values in the Google sheet by appending selected values whereas I want to edit the previously selected value since I use that value to generate a chart. For example I have a formula for googlefinance to generate stock current price based on a cell. That cell is generated from appsheet dropdown selection. If values from dropdown keeps appending then the formula does not work. Could you please assist me here. The dropdown is set up using valid If and the table name and column nameā€¦

Thank you so much

Please post screenshots demonstrating the unwanted behavior.