Green’s Dictionary of Slang

to lend a hand.

1705–07		N. Ward Hudibras Redivivus I:6 6: All strain’d their throats to bear a bob.
1772		Bridges Burlesque Homer (3rd edn) 85: For wives they no longer sob, / Finding that they must bear a bob.
[c.1786		Grose Classical Dict. of the Vulgar Tongue ms. additions n.p.: To Bear a Bob, to sing in Chorus. or Join in with any Singers].
1797		Bridges Burlesque Homer (4th edn) I 177: Alternately let’s take the swat; / Each bear a bob both night and day.
1809		B.H. Malkin (trans.) Adventures of Gil Blas (1822) I 282: We all of us bore a bob.