Green’s Dictionary of Slang

handle v.

[euph.]

1. [19C] to masturbate.

2. [19C; 1970s] to have sexual intercourse.

3. [1910s–40s] (US) to manhandle.

4. [1980s+] (S.Afr.) to believe, to find credible.

In phrases

handle up (v.)

[2010s] (US teen) lit. or fig., to get on with a task.