You can use a button to toggle a variable and use the variable to show/hide the input box. Create a variable vShow and give it an initial value of -1. Then add a Set Variable action to the button. Use vShow as variable name and =not $(vShow) as value. On the layout tab of the properties window of the input box enable the Conditional show option and use as expression =$(vShow). You can now show/hide the input box using the button. You can also make the text on the button depend on the variable: =if($(vShow), 'Hide input box', 'Show input box')
An alternatively might be to create a list of all possible (allowed) values which the user could chose per dropdown or scroll. Such listing could be applied manually or calculated. Have for this a look within the object-properties on the options in tab restrictions.