How can I switch the opam compiler in an easy way and what is the --set-switch flag?

Consider:

$ opam switch set ocaml-variants.4.07.1+flambda_coq-serapi.8.11.0+0.11.1
# Run eval $(opam env --switch=ocaml-variants.4.07.1+flambda_coq-serapi.8.11.0+0.11.1) to update the current shell environment

$ eval $(opam env --switch=ocaml-variants.4.07.1+flambda_coq-serapi.8.11.0+0.11.1)
[NOTE] To make opam select the switch ocaml-variants.4.07.1+flambda_coq-serapi.8.11.0+0.11.1 in the current shell, add --set-switch or set OPAMSWITCH

But then it doesn't tell me at all where --set-switch should go. Why? Where?

Related:

• Switch environment in OPAM