OK. in the "Start Date" field, rather than picking a value from the Dynamic Content list, switch to "Expression" and start typing the name of the function to be used, eg: format... then pick the "formatDateTime" expression from the list, add the opening bracket, then switch to "Dynamic Content" to select your date/time variable to be formatted. This will get inserted into the expression. Then add the rest of the expression parameters, ie: the desire format string.
Using "Expression" window and switching between it and the Dynamic Content window can sometime be fiddly, but it works. You can type in the whole expression *into the expression box* provided you get it 100% correct, then press OK and it will be inserted in the flow. You *cannot* just type an expression directly into a flow field!
For example, you could type this... formatDateTime(utcNow(),'dd/MM/yyyy')
into the box highlighted below, press OK and it would work. It will then appear in the flow field with a (sort of) red [fx] label
Good Luck
