You can print to your DYMO printer by installing WePrint (View) on your Mac or PC from here https://esz.nz/wp
WePrint is a free printer sharing server. The iPhone/iPad does not provide an option to connect to a printer via USB.
In the Print screen in Print, select your WePrint DYMO LabelWriter by tapping on the "Choose" (View) button.
Make sure you have selected the green WePrint printer icon with your DYMO printer name.

You can print address/shipping labels to your DYMO printer by tapping on "Contacts" in Print, select one or more contacts and tap on the Print button.

When you see the Print screen, tap on "Printer Options" to open the "Paper size". Tap on the "+" button in the top right to add your own custom label size.

You can also select either the work or home address option.

If you have the LabelWriter Twin you can select the right or left roll in the "Paper Tray" in the "Printer Options" screen.