Symbol menu in auctex math mode

Question

in AucTex math mode several symbold are already defined. Fom latex.el:

(defconst LaTeX-math-default
'((?a "alpha" "Greek Lowercase" 945) ;; #X03B1
(?b "beta" "Greek Lowercase" 946) ;; #X03B2
(?g "gamma" "Greek Lowercase" 947) ;; #X03B3
(?d "delta" "Greek Lowercase" 948) ;; #X03B4
(nil "sum" "Var Symbol" 8721) ;; #X2211
(nil "prod" "Var Symbol" 8719) ;; #X220F
(nil "coprod" "Var Symbol" 8720) ;; #X2210
(nil "int" "Var Symbol" 8747) ;; #X222B
(nil "oint" "Var Symbol" 8750) ;; #X222E)))

The characters with nil have no shortcut. How do I access them? Do I really have to redefine them in latex-mode-list?

The documentation of auctex and latex-mode-list[1] says:

First, the key to be used after LaTeX-math-abbrev-prefix for macro insertion. If it is nil, the symbol has no associated keystroke (it is available in the menu, though).

But how can I bring up this menu? And as a second question, what is the best practice to redifine the shortcut of already defined symbols?

Thanks!

EDIT:

From the comments:

1) The menu the manual is referring to is in the menu bar and just called Math.

2) Entries can be added by editing LaTeX-math-list, which will override an entry with the same symbol present in LaTeX-math-default.

[1] https://www.gnu.org/software/auctex/manual/auctex/Mathematics.html#Mathematics