Use logical indexing instead. You can do that without the for loop. (untested)
if ...
rowsdelt = app.UITable3.Data(:,app.ColumnNumberbeingevalulatedEditField.Value)>=Filter;
app.UITable3.Data(rowsdelt,:)=[];
end
Note that you'll want the delete command inside the if statement or you'll get an error about undefined variable rowsdelt anytime app.lowpassbutton.value is false.