Code to paste form data to next available row if cb1 value doesn't exist in column a

Hi there I have attached a spreadsheet with user form and vba which is almost working how I want but could do with some help finishing.

On sheet 4 I have a userform that looks up combobox1's value and then adds the value of textbox1 to the value of the of the cell in row 2 of the row looked up in combobox1.

This functions fine how ever if an item is not in the list named 'Wet product waste' it comes with an error and to debug. If the item is not in this list on the next available line I would like that value of combobox1 to be basted in colum a and then the value in textbox 1 to column b.

Hope this makes sense look forward to replies.

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