store form in cookie issue

I am wanting to store a from in a cookie for the purpose of as it is quite a large form ( around 50 elements ) I would like the user to be able to click a 'Save Form' input button and they can return at a later date to complete.

I have discovered from the behaviours window there is all the necessary behaviours ( store / set entire form to cookie )

From older posts to forum I saw one answered by Jason saying you should select the 'Input [submit]' button and bind the 'store entire form in cookie' behaviour to it.

Then select the body tag and bind the 'Set entire form to cookie' with the 'onClick' behaviour.

My problem is I can't edit the body tag as it is in the template which is un-editable and I can't find the 'make tag editable' feature which may have been removed from DW CC 19.

What are my options here?

Thanks in advance!