Hi, thats not a bad idea for a future update so the user can clean up their product master tab very quickly whenever they want... I will look into adding that in the future.
In the mean-time, you have a few options depending on your comfort in using excel.
The easiest way would be to:
Refresh your active item list.
Add a formula to the right side of your Product Master data (either in an unused column, or add a new column header).
Place a formula [if you are using item title to match] =match(C4, ActiveList!C:C,0)
[or if you are using SKU to match] =match(G4, ActiveList!M:M,0)
Then add an auto filter, filter by #N/A
Select all rows, right click, select Delete (or select rows and hit CTRL -)
Just save first
Let me know if you have any questions or need further help.