My little one got insect bite and now has a blister in his finger full of puss. How to safely break the blister?

Bring to pd pls!! My niece had a "pimple" on the nose and it was full of pus and swollen. It only went down when she got cream from PD and she had to take antibiotics! PD said it was likely a bite and not just a pimple like we thing it was. When it comes to kids I never fully depend on natural remedies because we don't know what are the causes