PyPlot Backend issue

For this issue:

julia> using Plots

julia> pyplot()
┌ Warning: PyPlot is using tkagg backend, which is known to cause crashes on MacOS (#410); use the MPLBACKEND environment variable to request a different backend.
└ @ PyPlot ~/.julia/packages/PyPlot/XHEG0/src/init.jl:192

How do I actually set the backend? Is it within the Julia REPL or elsewhere? On MacOS, what’s the recommended backend (to be installed by conda)?