Stay, ruby breasted warbler, stay
patient plume thy little wing
"Patient" as a verb means "be patient with" or "endure patiently." He's asking the bird to tolerate having its wing smoothed down while he talks—treating it like a fidgeting child.
Thy notes the blossoms charm to blow
"Blow" means "bloom" in period English. He's claiming the bird's song literally makes flowers open—the kind of nature-magic conceit that Romantic poets loved but Keats would later abandon.
make superiour each delight
The archaic spelling "superiour" appears in Keats's juvenilia. He's 18-19 here, still learning his craft, still spelling like his 18th-century predecessors.