I am new to pywinauto and I don't know how to use control identifiers.
How would I set No. of loops:
to 99999?
For dynamic edit box you can use label text as a part of identifier. Examples:
app.WindowName.No__of_loops_Edit.set_text('99999')
# or
app.WindowName['No. of loops:Edit'].set_text('99999')
# for more realistic typing char by char:
app.WindowName['No. of loops:Edit'].type_keys('99999')
It's described in more details in the Getting Started Guide (section "How to know magic attribute names").