find next blank cell within range

Hi again

I have a range C6:AD2506, this is my data entry range.
I have a user form with a button saying ' show me' which i want to take the user to the 1st blank cell within that range. Also when this is clicked I would like for it to remain visible so vbModeless and for the text on it to change to 'next'. And when clicked again it will go to the next blank cell, continuing until it has gone through them all.

Within my range C6:AD2506 i have mandatory fields. I only want the button to take the user to blank cells within these mandatory columns.

Also I dont want entirely blank rows to be included in the search. These are flagged up in the A column. For rows to be included in the search it says "Item" in the A column, for rows not to be included it will says "Item."

What code should I use for this set up?

Here is an attachment of the data entry sheet..the mandatory fields are marked with red cells.