Dropdown for customers to only add data to specified column and customer row

Hi Guys,

I am quite new to appsheet.
We created an google sheet with two tabs ref valeus and dropdowns.

Ref valeus = here i put all the customers information that we already have.
Dropdowns = our employees can selected/save here the customers the need to, from the ref valeus through forms.

So all the selected customers are in tab dropdowns, is possible that i send the selected customers an link/email so the can only add 1 or 2 dates in te right column and row? each customer have there own uniek customer number so hopefully we can use this to specify where the dates can be added by the customer.

Is this possible, if yes can you point me in the good direction.

already thanks.