Go to the dutyman page https://dutyman.biz/dmmain.aspx?id=Y0001457. It looks like this. If you can’t remember your login, you can get a reminder and there are help buttons.
When you have logged in the page will look like this. Click on ‘volunteer for a duty’ or one of the other action buttons.
The Volunteer for a duty page looks like this. Follow the instructions on the right hand side.
When you have selected a duty to volunteer for it will be highlighted. Duty details will be in the box on the right. Hit the Volunteer button.