Change Value of External Tags in WinCC 7.4

Hi,

Im trying to change the value of my external tag DB31, DW54. My plan is for the user to input the values in the I/O field and click a button to change the value of the external tag. My problem is I can only do it through left click event direct connection on the button but it can only change the value once. How do I do this dynamically in runtime?

Thanks,