Gantt chart estimation field

I'm trying to use YouTrack for the first very time to create a Gantt chart. I'm filling in the form.

There is an estimation field which is 'required', however it offers me no options to fill it in, so I cannot fill this field in and because it is 'required 'I cannot create the Gantt chart.

Can someone advise me what to do?

Thanks

Hannah

See the picture below